Preheat the oven to 200°C (convection oven). Put chestnut flour, sugar and vanilla sugar into a bowl. Start kneading with the electric mixer by adding milk until smooth. Add eggs and continue kneading with the electric mixer until homogenous.
Grease the ramekins (mini crostata ramekins with 12 cm in diameter) with butter. Alternatively, you can use a large oven dish of about 35 x 25 cm. Fill with the batter.