The Prague cake is a Soviet classic: chocolate layers, chocolate cream and glaze. The common failures are a cream that splits or turns greasy, and dry sponges. The first comes from butter and condensed milk at different temperatures, the second from over-baking.
What it is made of
Top to bottom:
- Dark ganache 0.5 cm
A glossy cap
- Chocolate sponge ×3 · 2.5 cm
- Condensed-milk buttercream ×2 · 1.0 cm
Three chocolate sponges, two layers of cream, ganache.
An honest note on how this differs from the classic. In the classic Prague cake the cream is chocolate (with cocoa or chocolate), the layers are brushed with apricot jam, and the cake is covered with a chocolate glaze. In this version the cream is plain butter with condensed milk, there is no jam, and the top is ganache. It tastes sweeter and milkier, and chocolate depth comes only from the sponges and the ganache. To move it closer to the classic, add chocolate or cocoa to the cream and a thin layer of jam, but the builder has no jam layer.
Order of work
Sponges (the day before): chocolate sponge with baking soda, because natural cocoa is acidic and soda deepens flavour and colour. Use fresh cocoa; old cocoa tastes bitter. Eggs, milk and butter at room temperature. Mix dry and wet separately, combine in 10 to 15 seconds. Fill the tin to two thirds. Bake at about 180 °C until a skewer is dry, plus 5 to 10 minutes to set the structure. 10 to 15 minutes in the tin, then a rack; never wrap warm. Chill 4 to 10 hours and slice with a wire.
Cream: all components at the same temperature. Beat the butter, pour condensed milk into the already beaten butter, and stop the mixer as soon as the colour evens out. Longer and it splits. If it has split: warm the bowl until the fat melts, cool and beat again.
Assembly:
- Moisten the sponge as needed (syrup or milk); in this version an unsoaked chocolate sponge can be dry.
- A thin even layer of cream, 3 to 5 mm, then the next sponge.
- Freezer for 20 to 30 minutes.
- Ganache: cream (30% or more) to 80 to 90 °C, chocolate, cold butter. Pour at 34 to 36 °C onto a cold cake.
Resting: a few hours in the cold; better the next day.
What can go wrong
- Grainy cream. Cold condensed milk into warm butter, or the other way round.
- Dry sponges. Over-baked or left uncovered too long.
- Dull ganache. Overheated, or the cream had too little fat.
- The cake slides. It was not chilled before the pour.
The verdict
Cream temperature and sponge moisture decide it. Moisten the sponge, chill the cake, and the ganache lays down smooth.