For the vanilla custard (we used instat custard mix following the instuctions in the package):
In a large bowl, dissolve the yeast in the milk, then add the egg yolk, the 1 1/2 tbs sugar, the salt and the flour.
Once everything is well incorporated, add the butter and knead well forming a soft dough.
Cover and let it rest in a warm place for around 2 hours.
Roll out the dough in a floured surface until it's around 1 1/2 cm thick, cut circles around 10 cm diameter from it.
Moisten the edges of one of the circles (at this point if you like a jelly filling, place a teaspoonful on the first circle) and lay another one
on top of it. Press firmly to seal the edges.
Place the circles in lined baking trays and cover, let it raise for around 2 hours.
Fry in a deep fryer at 190 °C for 4 minutes on each side or until browned.
Drain on absorbent paper and sprinkle with sugar.
For the vanilla custard:
Combine milk and cream in a small saucepan. Using a sharp knife, split vanilla bean in half lengthways and scrape out seeds.
Add bean and seeds to milk mixture. Place over medium heat.
Cook, stirring constantly, for 5 minutes or until hot (do not allow to boil). Remove saucepan from heat.
Whisk egg yolks, cornflour and sugar in a heatproof bowl until well combined.
Remove vanilla beans from milk mixture. Pour hot milk mixture over egg yolk mixture, whisking constantly.
Return mixture to saucepan over low heat.
Cook, stirring constantly, for 15 to 20 minutes or until custard thickens and coats the back of a metal spoon (do not allow custard to boil, as it might curdle).
Let it cool down, cover with plastic foil and refrigerate until cold before using.
Once the Krapfen are cold down, open a small hole in the middle and pipe the cream in the Krapfen.