Heat warm milk to 100℉, ensuring it's not too hot, or it may kill the yeast.

In a bowl, combine the yeast and warm milk, whisking until fully combined. Let it sit for 5 to 10 minutes until fully activated.

Add eggs, sugar, salt, and flour, then mix in a stand mixer until a dough forms.

Knead the dough for about 5 minutes, ensuring the ingredients are well incorporated.

Gradually add room temperature butter, ¼ cup at a time, mixing until fully incorporated.

Continue kneading until the dough comes together and no longer sticks to the sides or bottom of the bowl.

Transfer to a floured work surface, then shape into a ball and place in a greased bowl.

Cover and allow it to rise for about an hour, or until it has doubled in size.

Gently punch down the dough to release air and prevent over-expansion.

Shape it back into a ball on a floured work surface for an even texture.

Transfer it to a bowl, cover with plastic wrap, and place in the fridge for overnight proofing (about 8 hours).

Divide the dough into two equal portions for uniform donuts.

Use a bench scraper to cut each half into eight pieces, creating 16 equal-sized pieces in total.

Roll each piece into a ball or bun shape for even frying.

Place on a baking sheet lined with parchment paper, lightly dust with flour to prevent sticking.

Heat a pot with enough oil to submerge the donuts, keeping the stove temperature steady at 350℉.

Choose tallow, lard, or coconut oil for a rich flavor and crisp texture.

Use a slotted spoon to carefully place the dough buns into the oil, ensuring you don’t overcrowd the pot.

Fry about 4 at a time, depending on the size of your pot, to maintain even cooking.

Cook on one side for 3 minutes, then flip and fry for another 3 minutes until golden brown.

Transfer the donuts to a wire rack lined with a baking sheet and paper towels to soak up extra oil.

Roll the cooled donuts in a bowl of sugar to coat them evenly. Allow them to finish cooling before filling.

In a bowl, whisk together milk and eggs, then set it aside.

In a saucepan, combine sugar, corn starch, and vanilla, then pour in the milk and egg mixture along with butter.

Cook over medium heat, stirring constantly, until the mixture boils and thickens.

Reduce the stove to low and let it cook for another minute before removing the pan from the heat.

Cover the custard with plastic wrap, ensuring it touches the surface to prevent a skin from forming.

Refrigerate for 30 minutes to an hour to allow it to chill completely.

Once the custard and donuts are completely cooled, transfer the filling to a piping bag.

Alternatively, use a Ziploc bag by cutting a small corner off.

Use a knife or skewer to cut a hole into the side of each donut.

Insert the piping tip and fill each donut until slightly firm to the touch.