Warm the milk lukewarm. Dissolve yeast in it. Put flour, sugar, salt, oil and egg yolk in a bowl. Pour in the yeast milk and knead everything well with the dough hooks of the hand mixer. Cover and leave to rise in a warm place for 30-40 minutes.
Knead the dough again well and roll out 1/2 cm thick on a lightly floured work surface. Using a cookie cutter, mark about 12 hearts (9 cm wide) on half of the pastry sheet and place a teaspoon of jam in the middle of each heart.
Spread the edges of the marked hearts with egg white and fold the second half of the dough over them. Cut out the hearts, press the edges of the dough well and let it rise covered for another 15-20 minutes. Heat vegetable fat in a high pot or deep fryer to 180°C.
Slide two doughnuts in each case into the hot fat and bake for about 6 minutes until golden brown. After half the baking time, turn the hearts with a wooden spoon. Lift them out with a skimmer.
Drain on kitchen paper and let it cool down. Mix icing sugar and lemon juice and coat the donuts with it. Let dry on a cake rack. Arrange on a plate and decorate as desired with mint leaves.
Results in about 12 pieces.