Chop the white couverture and melt it with half of the butter in a double boiler.
Chop the dark couverture and melt it with the other half of the butter in a double boiler.
Beat the eggs together with the sugar until everything is whitish and frothy, divide the sugar-egg mixture in half. Stir the white couverture into one half and stir the dark couverture into the other half.
Then stir in 125 g of flour into each dough, then add 100 g of walnuts.