Yeast mixture:

Cup of Yum
1. In a large bowl, whisk the warm milk with the room-temperature egg, once combined add the instant yeast. Whisk fully until dissolved.

Donut dough:

1. Then, add sugar, flour, and salt to the yeast mixture. Use a spatula to mix until combined and after that knead with your hands until all flour has been incorporated.
2. Next, add the softened butter and work it in with your hands until the dough is smooth.
3. After that, transfer the sticky dough ball into a large lightly oiled bowl and cover it with plastic wrap. Place it in a warm place and let it rise for a few hours until it is about two to three times its starting size. Transfer the dough onto a flat, lightly floured surface and knead for two to three minutes.

Chocolate custard:

1. First, add the sugar, egg and yolks, cornstarch, cocoa powder, and salt in a bowl and whisk until thick and smooth. Set it aside.
2. Add the milk and vanilla to a medium saucepan and heat over medium-high heat until it just starts to boil. Remove it from heat. Remove it from heat.
3. Slowly and WHILE WHISKING CONSTANTLY pour the hot milk, into the egg mix, and whisk to temper the egg mixture.
4. Once fully combined, transfer the mixture back to the saucepan over medium heat, and whisk vigorously until it starts to thicken, in about 2 - 5 minutes.
5. Lower the heat to low and immediately add the chopped chocolate. Whisk until the chocolate is completely melted.
6. Remove from heat and stir in the butter until melted and combined.
7. Transfer the chocolate custard to a bowl and immediately cover the surface with plastic wrap, ensuring the plastic wrap touches the whole surface. This is to prevent custard skin from forming on top.
8. Let the custard cool to room temperature and after that refrigerate it for 2-4 hours, should be completely chilled.

Shape the donuts:

1. In the meantime, punch the dough and then transfer it to a lightly floured surface. Fold it a few times and divide it into eight equal pieces.
2. Shape each piece into a ball and place it on a baking sheet covered in parchment paper. Repeat with the remaining pieces. Make sure they are not too close to each other on the baking sheet. Cover them with plastic wrap and let them rest for 30 to 40 minutes.

Deep frying the donuts:

1. Place a large, deep pan with about 1 1/2 - 2 inches of oil over low-medium heat. Bring the oil to 350 degrees F. Add a few donuts at a time and fry them for 1-2 minutes on one side, or until golden brown. Flip and repeat.

Fill:

1. After the donuts have cooled completely, poke a hole, using a long rounded object, like a chopstick. Place a bowl with about one cup of sugar next to you. Then roll them in sugar until covered on both sides.
2. Transfer the chocolate custard into a pipping bag, cut a small hole at the end, and fill the donuts with custard until you have just a little ball of custard on the surface.