Butterkekskuchen mit Puddingfüllung (icebox butter biscuit cake with pudding cream)

Method

1. Line a loaf tin, about 25 by 11 cm, with cling film, leaving plenty of overhang on all sides to lift the cake out later.
2. Whisk the sugar, cornstarch and egg yolks into a small amount of the cold milk until smooth, in a bowl.
3. Heat the rest of the milk in a pan until steaming, then whisk it into the cornstarch mixture. Return everything to the pan.
4. Cook over medium heat, whisking constantly, until it thickens to a heavy custard that holds a trail off the whisk, about 5 minutes once it starts to thicken. Take off the heat, stir in the vanilla, and press cling film directly onto the surface to stop a skin forming. Cool to room temperature.
5. Beat the softened butter until fluffy, then beat the cooled pudding into it a spoonful at a time, until light and smooth. This is what gives the filling enough structure to hold a slice.
6. Dip each biscuit briefly in milk, a second or two per side, just enough to soften without falling apart, and line the base of the tin. Spread a layer of the pudding cream over the top. Repeat, alternating biscuits and cream, finishing with a layer of dipped biscuits on top.
7. Chill at least 3 hours, until firm. Melt the chocolate and butter together, gently, and pour over the top once the cake has set. Chill again until the glaze hardens, then lift out using the cling film overhang and slice.

Method in the Thermomix

Written for a TM5 or TM6, 2.2 litre bowl. This covers the pudding cream; the layering and chilling are the same as the hand method.

1. Milk, sugar, cornstarch, egg yolks and vanilla into the bowl. Cook 8 min / 90 °C / speed 3, until thickened. Pour into a bowl, press cling film onto the surface, and cool to room temperature.
2. Wash the bowl. Beat the softened butter for 20 sec / speed 4 until fluffy. Add the cooled pudding gradually with the blades running at speed 3, until light and smooth.
3. Layer and chill as in the hand method. The machine has no role in the dipping, assembly or glaze.

Notes

• Dip the biscuits briefly, not long. A second per side is usually enough; soaked too long they turn to paste and the layers collapse into each other instead of staying distinct.
• Do not skip beating in the butter. A pudding alone, without butter, is too soft to hold a cake together and the layers slide when sliced; the butter is what turns it into something closer to a buttercream.
• A genuine 3-hour chill is the minimum, and overnight gives a cleaner slice still. Cutting it too early leaves the layers soft and unstable.
• It keeps for 4 days in the fridge, covered, and the flavour and texture both improve slightly after the first full day.

Ingredient substitutions

• Butter biscuits work best for the classic texture; digestives or a similar plain biscuit are a reasonable substitute with a slightly different flavour.
• Dark chocolate glaze can be milk chocolate for a sweeter finish, or omitted entirely with a dusting of cocoa powder instead.
• A layer of sliced bananas or berries between the biscuits and pudding is a common addition if a fruit version is wanted.
• For a coffee-flavoured version, dip the biscuits in cooled strong coffee instead of milk, in the style of a German or Austrian icebox cake.