Preheat an oven at 180° C.
Cut the sponge cake into half inch slices and arrange them in a baking dish. Boil water in a non stick pan and put the lid over it.
Whisk together eggs, egg yolk, milk, cream and sugar in a bowl.
Remove the lid from the pan, place the bowl with egg mixture over the boiling water, and whisk till the mixture becomes light.
Remove from the boiling water, add dark chocolate and whisk well. Add butter and whisk.
Pour this mixture over the cake slices. Press lightly. Bake in the preheated oven for 20 minutes. Remove from the oven.
Garnish with strawberry jam and serve.