Second Helpings #23 White Mocha Custard Tart

A seriously caffeinated custard tart

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Last weekend I went to the London Coffee Festival and, besides consuming way too much coffee, I came away with a bottle of coffee concentrate from Climpson and Sons, one of my favourite London coffee roasters. I mainly used it to make iced coffee all week long but I also knew I wanted to make something with it, what better way to highlight the coffee than use it to make a custard tart. The concentrate I used is a little weaker than espresso so, if you are brewing the coffee yourself at home, you want something nice and robust. You can use any form of black coffee but make it nice and strong.

The tart is pretty simple and straightforward, even if it does have a few elements. The pastry is a classic French-style sweet pastry, pâte sucrée to give it its proper name, made with icing sugar and ground almonds to make an especially light and delicate pastry. The filling is a classic egg custard made with cream, sugar, egg yolks and, in this case, a lot of coffee. To add another layer of flavour and to give it almost a white mocha vibe, a thin layer of white chocolate ganache is added to the baked custard and decorated with stripes made of cocoa powder. The chocolate I used comes from Islands Chocolate, a British bean-to-bar chocolate company. Now before the white chocolate haters come out of the woodwork and tell me that white chocolate is too sweet and not even ‘real’ chocolate, let me tell you a little bit about this new, very special, white chocolate. Disclaimer, Islands sent me a sample of this chocolate to play around with but this is all my opinion and in no way an ad.

Most white chocolate tastes sweet and maybe with a hint of vanilla, but not much else. It would be hard to taste any cocoa flavour in most white chocolate, but why? Well, the main ingredient of white chocolate, other than sugar, is cocoa butter and the flavour of white chocolate should really come from that butter. The problem, though, is that most cocoa butter sold to make chocolate (and things like beauty products) is of very low quality and comes riddled with off-flavours that you wouldn’t want in your chocolate, think of cheesy off-milk. Because of this, the cocoa butter goes through a process called deodorisation, a process that removes, not only the off flavours but, all the flavours naturally present in the cocoa butter. This results in white chocolate that is sweet but not much more. Because Islands Chocolate doesn’t buy mass-market cocoa butter, but buys it directly from partner farms, the butter they use is left unrefined meaning all the flavours naturally present in the cocoa butter end up in the final product. What does that mean for the flavour, well it means it tastes so much more complex than most other white chocolates, helped along by a very small amount of salt as well. It has so much flavour of cocoa that I have been able to confuse people into thinking it’s actually milk chocolate. I got a bunch of friends to taste it blind and many of them thought they were eating milk chocolate, amazing!

Before we get to the recipe let me just briefly talk about eggs, because this recipe uses a lot of them! When making a baked custard like this there are four ways to use eggs to set the custard; yolks only, whites only, whole eggs only, or a combination. Using all yolks, as I do in this recipe makes a custard that is rich and creamy but that barely sets, it’s soft and creamy and incredibly unctuous. If you made it with all whites the custard would be more gelatinous and firm and of course less rich and creamy. Using whole eggs or a combination of yolks and whole eggs gives you something in between. For this recipe, I chose whole yolks because I wanted the creamiest, silkiest custard possible but you can play around and adapt it as you wish. For example, if you want the custard to be a touch firmer, and slightly more set, I would use 6 yolks and two whole eggs.

To make this tart you will need a 23cm wide 3cm tall tart tin, with a removable base.

White Mocha Custard Tart
Serves 12

Sweet Pastry

200g plain flour

20g ground almonds

35g icing sugar

1/4 tsp fine sea salt

125g unsalted butter, diced and chilled

1 large egg yolk

1/2 tbsp ice cold water

Coffee Custard Filling

450ml double cream

150ml strong black coffee, cooled

1 tsp vanilla bean paste

125g light brown muscovado sugar

10 large egg yolks

White Chocolate Glaze

150g white chocolate, finely chopped

100ml double cream

Cocoa powder, for decoration

For the pastry add the flour, almonds, sugar and salt to the bowl of a food processor and pulse to combine. Add the diced butter and pulse until the mixture resembles breadcrumbs. We are not making a flaky pastry so you want to fully combine the butter, no big chunks here. Mix together the yolk and water and drizzle into the food processor. Pulse until the mixture starts to clump together, stopping before the pastry forms a ball; processing the dough too much at this stage over develops the gluten and can make a pastry that is tough and prone to shrinkage. Tip the pastry out onto the work surface and use your hands to bring together into a ball. Press the pastry into a flat disc and refrigerate, for at least an hour but preferably overnight, before using; an overnight rest will make the pastry easier to handle, so if you have the time its worth making in advance.

If you don’t want to make the pastry using a food processor you can make by hand, it will just take a little longer. Follow the above instructions but use your fingertips to rub the butter into the flour mixture and use a knife to mix in the egg yolk mixture.

On a lightly floured work surface roll out the pastry until it is about 3mm thick. Carefully drape the pastry into a 9-inch loose-bottomed tart tin, trimming away the excess. Pop the tart case into the freezer for 30 minutes whilst you preheat the oven to 210ºC (190ºC Fan). Line the tart case with a crumpled piece of parchment paper (the crumpling makes it sit flush with the pastry) and fill the case with baking beans or rice (I prefer baking beans because they’re made from ceramic they transfer heat to the pastry better than rice so the pastry bakes more evenly. Pop the. Tart on a baking tray and bake in the preheated oven for 20 minutes. When the time is up carefully lift out the baking beans and place the tart back into the oven for another 5-10 minutes until the base is evenly browned.

As we are baking a custard tart, at this stage you can do an optional step to help ensure a crisp pastry base with no soggy bottoms in sight. Once the tart case is fully baked you can brush the inside of the tart with either egg yolk or egg white and pop the base back into the oven for a minute for this to set. This layer acts as waterproofing stopping the moisture from the custard seeing back into the pastry. Egg yolk works best for this but as the recipe uses a lot of yolks already you will have whites that need using up and they still do a good enough job at protecting the pastry.

Turn the oven down to 120ºC (100ºC Fan).

For the filling place the cream, coffee and half of the sugar into a saucepan and bring to a simmer. Meanwhile, place the egg yolks and remaining sugar into a large bowl and whisk together until the mixture is smooth. Pour the hot cream mixture over the yolks, whisking as you do so to prevent the mixture from curdling. Pour the custard through a fine mesh sieve into a large jug and set aside until the oven has cooled down to the desired temperature.

Place the tart back into the oven, still sitting on a baking tray to make it easier to manoeuver. Carefully pour in the filling, it should reach the very top of the pastry, and bake for about 80 minutes or until the correct level of jiggle is achieved. To test that the tart has finished baking you need to give the tart a gentle shake to see how the custard moves. When underbaked the custard will move like a liquid but when it is baked it will jiggle more like jelly, it will have a gelatinous shimmy and be just set around the edges. Once fully baked from the oven and set aside to cool for an hour before transferring to the fridge to chill fully.

For the glaze add the chocolate and cream to a small pan and place over the lowest heat and cook, stirring constantly until the chocolate has melted and you have a smooth pourable ganache. Pour atop the tart and spread into an even layer that covers all of the custard. Refrigerate until the glaze has set.

For the decoration cut out strips of paper and layer them atop that tart, set evenly apart. Dust with cocoa powder then remove the strips of paper, living behind a striped pattern atop the tart. Kept refrigerated the tart will keep for 2-3 days.