Mix flour, milk and eggs. Add vanillin sugar, icing sugar and orange liqueur. Cover the dough and let it rest for about 30 minutes. Bake 8 wafer-thin pancakes one after the other in a lightly greased pan and fold them into quarters.
For the sauce, heat butter in an ovenproof dish and stir in icing sugar. Deglaze with orange juice and season with orange liqueur. Place crêpes in the sauce. Warm the cognac in a ladle, light it and pour it over the crépes.
Serve hot. Makes 8 crepes.