Vanilla Patisserie Slices Questions

My sponge came out flat and dense - what went wrong?

The lift here comes almost entirely from the eggs, since there is only a small pinch of baking powder. Beat the eggs and salt first, then add the sugar gradually and keep beating a full 5 minutes until the mass is pale and airy. After sifting in the flour and cornstarch, fold gently rather than stirring, or you knock out the air you just whipped in.

Can I use something other than cornstarch in the pudding cream?

Cornstarch does the thickening in both the sponge and the cream, so swapping it changes the texture. In the pastry cream you can use the same weight of another starch such as potato or tapioca starch, but whisk it into the cold 100 ml of milk exactly as written so it dissolves without lumps. In the sponge, replacing the 20 g cornstarch with flour works too, though the crumb turns a little less tender.

Why did my buttercream curdle when I added the pudding?

This is almost always a temperature problem: the butter must be soft and at room temperature, and the pudding must be fully cooled before they meet. Add the pudding to the beaten butter spoonful by spoonful, letting each addition emulsify before the next. If it does split, let the bowl sit at room temperature for a few minutes and beat again until smooth.

How far ahead can I prepare the parts?

The pastry cream is the natural make-ahead component - cook it, cover the surface directly with cling film so no skin forms, and chill it, then bring it back toward room temperature before beating it into the butter. The sponge can also be baked ahead and kept wrapped so it does not dry out. Assemble, dust, and give the finished slices their minimum 1 hour chill before serving.

How should I store the finished slices, and when do I dust them?

Keep them covered in the fridge, since the filling is a butter-and-egg-yolk pastry cream. Dust with powdered sugar shortly before serving rather than days ahead - on chilled slices the sugar slowly dissolves and the crisp white finish disappears. Cut the slices with a clean knife after chilling so the cream layer stays sharp-edged.