Preheat the oven to 200C/390F (180C/355F fan). Add the sugar, eggs and vanilla extract together in a bowl. Whisk until pale, thick and fluffy. Fold in the flour and combine.
Line the tin with grease-proof paper - you can use a few dabs of batter to help stick the paper in place. Pour 1/3 of the batter into the tin and gently spread evenly. Bake for 8 minutes until just firm.
While the sponge is still warm, tip face down onto a fresh sheet of baking paper and remove the baking paper. Use the remaining batter to make two more sheets of sponge.
For the strawberry sauce
Stem and quarter the strawberries (use the drinking straw trick if you like), then cut those pieces into halves. Rinse and drain well, then put them into a saucepan along with the sugar, cornflour, vanilla extract and lemon juice.
Cook over a medium heat for 20 minutes, stirring occasionally until thick. Allow to cool to room temp.
For the custard
Add the eggs, flour, sugar, vanilla essence and splash of the milk in a large bowl. Whisk together the until smooth. Warm the rest of the milk to almost boiling, then pour into the egg mixture, stirring vigorously.
Pour the mixture into a clean pan and heat gently for about 25 minutes, whisking gently until thick. Pour into a clean bowl, cover the surface with plastic wrap and leave to cool to room temp.
To construct
Start with a few spoonfuls of stewed strawberries to just coat the base of the dish. Then put down your first sponge layer. Add approximately one third of the custard over the sponge. Spread it out with a spoon to cover the entire sheet.
Spoon half of the remaining strawberries into the tin.Followed by another sponge layer. Add another layer of custard using half the remaining mixture.
Repeat the pattern one more time, then sprinkle grated white chocolate all over the top to finish.