PASTRY CREAM PREPARATION
Heat the milk with the vanilla. In a mixing bowl, combine the cornstarch, sugar, and eggs. Whisk well.

Once the milk is hot, slowly pour it over the cornstarch mixture while whisking. Leave about a quarter of the milk in the saucepan, then pour the bowl mixture back into the saucepan.

Cook over low heat, whisking constantly, until the cream thickens.

Transfer the cream to a bowl and cover directly with plastic wrap (make sure the wrap touches the surface) to prevent a skin from forming. Let cool, then refrigerate.

Preheat the oven to 350°F (180°C).

SPONGE CAKE PREPARATION:
Mix the flour with the baking powder. Separate the egg whites from the yolks, and beat the egg whites until stiff peaks form.

When the egg whites are firm, add the sugar and beat again. Lower the mixer speed and add all 4 egg yolks at once, then immediately add the flour and baking powder mixture.

Stop the mixer quickly so the batter doesn't deflate. Pour into the prepared pan, smooth the top, and bake right away for 20 to 23 minutes at 350°F (180°C) with convection if possible.

FILLING:
Cut the peaches into small pieces.
Place them in a skillet with the sugar and a splash of lemon juice.
Cook until the peaches are soft and syrupy, then let cool.

Once the cake is baked, remove it from the pan while still warm and let it cool completely before slicing in half.

Whip the heavy cream into stiff peaks. Take the pastry cream out of the fridge and gently fold in the whipped cream.

ASSEMBLY:
- Brush the sponge cake with orange juice.
- Spread half the pastry cream on one layer, then add the peach pieces.
- Place the other cake layer on top.
- Using an offset spatula, spread the remaining cream over the top and sides (reserve some cream for decorating with a piping bag) and smooth it out.
- Press toasted sliced almonds onto the sides of the cake.

Cut the peach into wedges and decorate the top.
- Fill a piping bag with the remaining cream and pipe decorations on top of the cake as well.