Preheat the oven to 180°C.
Grease, flour, and line a 23cm spring-form cake tin.
Whisk sugar, eggs, and lemon zest in a bowl over simmering water until doubled in volume.
Gently fold in the flour into the egg mixture in two stages.
Fold in the melted butter carefully.
Bake for 25-30 minutes and then cool on a rack.
Boil milk with a split vanilla pod.
Whisk eggs, sugar, kirsch, and cornflour in a separate bowl.
Sieve hot milk into the egg mixture and whisk.
Cook the custard over medium heat, stirring constantly until very thick.
Stir in butter and chill until firm.
Boil lemon juice, sugar, and 70ml water to make syrup.
Roll out a 23cm marzipan disc.
Slice the sponge in half horizontally.
Line the tin with acetate and place the first sponge layer inside.
Brush with syrup and arrange halved strawberries around the edge.
Pipe crème pâtissière over the base and between the strawberries.
Fill the center with quartered strawberries and more crème pâtissière.
Add final sponge layer, brush with syrup, and top with marzipan.
Chill to set, then decorate with chocolate and reserved strawberries.