Preheat oven to 250 degrees, roll out both slices of puff pastry, brush with a little bit of butter and place sheets on top of each other. Roll into a roll from the long side and cut 18 even slices (about 1.5 cm wide). Butter muffin tin and press slices into it, lining the edges.
Bring the milk and whipping cream to the boil with the butter, then gradually sift in the flour mixed with sugar and salt, stirring heartily. Boil briefly and remove from the stove, cool a little. Mix in the egg and the yolks and the vanilla sugar or the scraped out pod. Bake for about 11-12 minutes on the bottom rack, then 2-3 minutes on the top rack.
Carefully remove from the mold and sprinkle with a little bit of cinnamon.