First, make the cream. Pour 2 1/2 cups (600 ml) of milk and the sugar in a suitable container.
Beat the eggs with the remaining milk and add the flour slowly. Beat with the well beaten flour (strain through a sieve if not well beaten enough) to obtain a homogeneous mixture, and in turn a nice, smooth cream without lumps.
Once the milk comes to a boil, pour the egg mixture in a thin trickle. After the cream thickens, add the butter and vanilla. Continue stirring until the butter is completely dissolved and absorbed into the cream.
Use a large bowl to assemble the cake. Wrap it with plastic wrap and start arranging the croissants, cut in half, lengthwise along the bottom of the bowl.
Then put a layer of cream, layer of strawberry jam, croissants again, cream, jam... and finish off with croissants. Cover with foil and leave in the fridge overnight.
After the cake has sat overnight and firmed up, invert it onto a plate, sprinkle with ground walnuts or other nuts.