For about 24 krapfen
Ingredients for the dough:

200ml milk
100g sugar
30g fresh yeast
300g rice flour
100g rise starch
100g potato starch
1 egg
3 yolks
50ml vegetable oil
Grated rind of 1 lemon
1 packet of vanilla-flavoured sugar
1 pinch of salt
1C of rum

Procedure

For the dough starter, blend the milk carefully with the crumbled yeast, the sugar and a tablespoon of flour. Cover and let rise in a warm place until doubled in volume. Mix the flour in a bowl with the starches, egg, and lemon zest, vanilla-flavoured sugar, salt and rum. Add the starter and knead until bubbles form. Cover the dough and let rise in a warm place for about an hour. Knead again and cut into 24 equal pieces. Shape smooth balls and place them on a cloth sprinkled with flour. Cover and let rise for another 20 minutes.
Ingredients for the custard filling:

5 yolks
1 pinch of salt
100g rise starch
1 vanilla pod
750ml milk
180g sugar

Procedure

Whisk the yolks, salt and rice starch thoroughly. Open the vanilla pod and bring the pulp to a boil with the milk and sugar. Add the mixture of yolks and flour, stirring constantly until the custard begins to boil gently and thicken. Pour the vanilla custard into a bowl, sprinkle with sugar (so it does not form a skin) and let it cool.
To finish

Heat the oil for frying the krapfen to about 160 degrees. Place the krapfen in the boiling oil, top down. Cover and cook until the krapfen are a nice golden brown. Turn and cook on the other side, uncovered. Drain the krapfen on paper towels. Fill a pastry bag with the vanilla custard and fill the krapfen generously, then sprinkle with powdered sugar and serve.