For the doughnuts, mix the yeast with 6 tablespoons of lukewarm water and leave to rise for 5-7 minutes. Warm the milk lukewarm. Knead both with 175 g flour, 1 pinch of salt and the remaining dough ingredients using the dough hooks of the mixer.
Gradually knead 175 g flour until a moist dough is formed. Cover and leave to rise in a warm place for 1-1 1⁄2 for hours until the dough volume has doubled.
Line two trays with baking paper. Roll out the dough on a little flour to a thickness of about 1 cm. Cut out approx. 15 circles (each approx. 8 cm Ø). Knead the dough again if necessary and roll out again. Place the circles on the trays at a distance.
Cover and leave to rise for about 45 minutes.
For the caramel, caramelise sugar and 6 tbsp. water over medium heat until golden. Stir in butter and cream (may splash!) and season with sea salt. Set aside. Stir the ingredients for the filling until smooth.
Pour into a piping bag with a small perforated nozzle. For the cinnamon sugar, crumble the biscuits and mix with the remaining ingredients.
Heat the oil to approx. 140 °C for frying. Fry the dough circles in portions for 3-4 minutes until golden brown, turning once. Lift out and immediately roll in cinnamon sugar. Prick the doughnuts from two sides one after the other with the punched spout and press in a good 1 teaspoonful of the filling.
Serve warm with caramel and any remaining cinnamon sugar.