Warm 1/2 cup milk and 1/2 cup heavy cream in a saucepan. Bring to a boil, then remove from heat, cover and let stand 10 minute
In a large bowl, whisk the egg yolks and sugar until creamy, then beat in the flour. Add cream mixture and vanilla extract to egg mixture and mix until smooth. Pour back into the saucepan and stir or whisk gently over low heat until the custard thickens.
Remove from heat and let custard cool by pouring it into a wide bowl and tearing off some wax paper, wetting it, then covering the bowl with it. This stops the custard from forming a skin. Do not put in the refridgerator.
When custard is cool, make ganache. Warm 1/2 cup plus 2 tbsp heavy cream, 1 tsp vanilla extract, and 1 tsp butter with chocolate (chopped into small pieces) and bring to a boil in a thick- bottomed saucepan. Remove from heat and whisk till smooth and thickened. Let cool a little before using, but it should still be runny enough to ice with.
Tear off four strips of wax paper or parchment and arrange in a square on the plate on which you're serving the cake. Sit one of the cakes on top and spread with cooled custard, then top with second cake. Dollop spoonfuls of chocolate ganache icing on top, letting it spread and drip down the sides of the cake.
When the entire confection is cooled and set, remove the strips of wax paper for a drip-free presentation plate.