Sour Cherry and Pistachio Eclair Cake

Aka Polish Karpatka

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For this weeks baking adventure, we are taking a trip to Eastern Europe, to Poland to be precise. The first time I came across this cake, it didn't quite look like todays cake, it was a modern version, an interpretation called an ‘Eclair Cake’. The cake was two sheets of choux pastry, filled with vanilla custard and topped with chocolate. The idea caught my attention and, after a little digging, I realised it was likely inspired by a more traditional recipe from Poland, Karpatka. The traditional version is two discs of choux pastry sandwiched with a custard-type filling and finished simply with a light dusting of icing sugar, most often served with coffee. The form of the cake is so unusual that I really wanted to recreate it myself.

Karpatka is named after the Carpathian mountains, Karpaty in Polish, and you can kind of see why. When the choux is baked, as large discs, it rises in an irregular and erratic manner, creating a whole bunch of peaks and troughs, the name seems obvious. In some versions, the bottom layer of choux is replaced with shortcrust pastry but from what I can see, the double choux version seems more popular. From my research, it seems like this cake originated in the 50’s or 60’s and so much is its popularity, you can even buy a boxed mix version, which I actually found in my local polish supermarket, here in London. I can’t find much of an origin story for this cake, but it does feel related to the napoleon, a puff pastry and custard affair, it also feels like there is a direct line between the paris-brest and the karpatka, both use choux pastry and both use a version of the same filling. Regardless of its origin, the combination of choux pastry and custard based fillings is a winning formula.

The filling is a cousin to last weeks ‘ermine’ frosting but a little richer. Instead of a simple milk based roux. this starts out with a thick pastry cream (so the milk roux plus eggs) and, once chilled, that is combined with butter and whipped to form a light buttercream like texture. This mixture is classically known as either German Buttercream or Crème Mousseline. This frosting is rich and silky smooth, but just like Ermine Frosting it isn’t too sweet and like its cousin, it has the ability to adapt to different flavours incredibly well. The frosting is made with a large proportion of milk and this is, of course, a brilliant carrier of flavour; using an infusion is a brilliant way to take this recipe and pump it full of flavour. On the other hand, the buttercream already has a wonderful custardy flavour and sometimes, that simplicity is all you need. For this recipe, I stuck with the classic vanilla recipe because I had plans to add other flavours in another way and wanted a more neutral base to play off against.

As we are already in the culinary world of Poland, I thought of adding another element, something popular in the region, sour cherries. I love sour cherries but, they are notoriously hard to find in the UK. I have occasionally had some luck at Polish or Turkish delis (Poland and Turkey are two of the biggest producers of sour cherries) but generally I use either sour cherry jam (this version is nice and sharp) or bags of frozen sour cherries, which I can thankfully find with much more regularity (there are multiple shops I know of locally, in East London, that sell the same brand, Natural Cool). If the sour cherries prove elusive, this recipe would also be fabulous with regular sweet cherries, I would simply dial back to the sugar and add a couple drops of almond extract, to add a bit of the sharpness and flavour found in the sour varieties.

The final addition to my version of the Karpatka is not at all polish or in any way traditional, I just love the combination and thought it would make an exceedingly delicious version. I am talking about Pistachio spread. A kind of pistachio Nutella, these jars of deliciousness are the sort of thing we all bring back from holidays in Italy, and then do nothing more with it than eat it directly from the jar with a spoon. Whilst there is absolutely nothing wrong with that plan, this is really nice way to use the spread to create a really fun recipe.

The cake itself is made with a relatively classic choux pastry. I say relatively because, other than one ingredient, it is my basic choux formula. This version uses a very small amount of baking powder, something that appears in many classic recipes for Karpatka. I tested the recipe with and without the baking powder, the version with the baking powder had a slightly improved texture, being a little lighter with more dramatic peaks.

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