If you've never tried krapfen before, get ready to fall in love with these fluffy, slightly chewy jam-filled donuts. They'll turn your home into a sweetly scented bakery!
Pour the lukewarm milk into the bowl of a stand mixer. Add the yeast and 1–2 tablespoons of the sugar. Stir the mixture gently and allow it to sit for 2–3 minutes until it is foamy.
Add the remaining sugar, softened butter, egg yolks, vanilla, and salt. Combine the mixture on low speed. Add the flour and knead on medium speed for 8 minutes, or until the dough is smooth and elastic (don't worry if it's slightly sticky).
Transfer the dough to a large greased bowl and cover it with plastic wrap. Let the dough rise until it doubles, about 45–60 minutes.
Lightly flour a clean work surface. Turn the dough out and gently knead it to remove air bubbles. Roll it out to ½-inch thickness. Cut out 16 rounds with a 3-inch cutter.
Place the donuts on a floured surface and loosely cover them with plastic wrap. Allow them to rise for 30 minutes, or until they are puffy.
Heat the oil in a large pot to 320°F. Fry 2–3 donuts at a time for 3 minutes, then flip and fry them for another 2 minutes. Transfer the donuts to paper towels to drain excess oil. Allow them to cool slightly.
Fill each donut with jam using a piping bag fitted with a long tip.
Dust the donuts with powdered sugar and serve them fresh. Enjoy!