For the shortpastry kneed sugar, butter and flour together and chill for at least 30 minutes in the fridge.
Cook blueberries with sugar until gooey.
Prepare a vanilla custard. Cook 100 ml milk with vanilla paste. Stir custard powder and sugar and remaining milk. As soon as the milk cooks stir in the custard powder and remove the pan from stove.
Preheat oven to 190°C.
Cut out squares each 9 x 9 cm or smaller. You need two for one handpie. Coat the half with eggwhite and ad some blueberries and vanilla custard. Cut out a small hole from the other squares. Cover each square with blueberries and custard with another square (with the hole). Pinch the edges (with a fork). And coat with eggyolk. Lay on a baking sheet an bake for 15 minutes or until golden.