Bring 1/8 litre water, fat and salt to the boil. Add the flour at once and stir until it comes off the bottom of the pot as a lump. Put the dough into a bowl, stir in 1 egg immediately, let it cool down a bit and knead in the remaining eggs bit by bit.
Add baking powder at the end. Pour the dough into a piping bag with star-shaped spout. Spray 8 equal-sized tufts onto a baking tray lined with baking paper and bake in a preheated oven (electric range: 200°C/ gas: level 3) for 20-25 minutes.
Cut off the lid of the cream puffs immediately with scissors and let the pastry cool down. Whip cream, sugar, vanilla sugar and cream stiffener until stiff. Sort blueberries, wash briefly. Puree half and stir into the cream.
Pour cream into a piping bag with a star-shaped spout and squirt onto the lower halves of the cream puff. Sprinkle remaining blueberries on the cream. Place the lid on top. Dust the cream puffs with icing sugar and serve, possibly decorated with mint leaves.
Results in 8 pieces.