Put flour, baking powder, salt, sugar and 1 sachet of vanillin sugar in a bowl. Add the egg, milk and oil and work into a smooth dough with the whisk of the hand mixer. Wash blueberries if necessary, drain and carefully fold into the dough. Grease the moulds (7 cm Ø; 150 ml content) and dust with flour. Pour the dough up to the rim and bake in the preheated oven (electric range: 175 °C/ gas: level 2) for approx. 35 minutes.
Let the muffins cool down for about 10 minutes and turn them out of the cups. In the meantime, whip cream until semi-stiff and pour in the remaining vanilla sugar. Fold in egg liqueur and serve in a small bowl. Arrange the muffins on a plate and serve