In a large mixing bowl, combine 4 cups of all-purpose flour, ½ cup of granulated sugar, 2 teaspoons of active dry yeast, and 1 teaspoon of salt. Warm 1 cup of milk and mix in ¼ cup of melted butter, 2 eggs, and the seeds from 1 vanilla bean. Gradually add this mixture to the dry ingredients, mixing until a smooth dough forms. Knead for about 8-10 minutes until elastic, then cover with a cloth and let it rise for about 1 hour, or until doubled in size.

Once the dough has risen, turn it out onto a floured surface and roll it out to about ½ inch thickness. Use a donut cutter to cut out shapes, making sure to create holes in the center. Arrange the cut donuts on a floured baking sheet, ensuring they don’t touch. Cover and let them rise for an additional 30 minutes until puffy.

In a medium saucepan, combine 2 cups of milk, ¾ cup of sugar, 4 egg yolks, and ¼ cup of cornstarch. Cook over medium heat, stirring constantly until the mixture thickens and begins to bubble, around 7-10 minutes. Once thickened, remove from heat and stir in the seeds of 1 vanilla bean. Transfer to a bowl, cover with plastic wrap, and let it cool.

In a deep pan, heat vegetable oil to 350°F. Carefully place the risen donuts into the hot oil, frying them in batches to avoid overcrowding. Fry each donut for about 2-3 minutes on each side until golden brown, then remove them to paper towels to drain excess oil.

Once the donuts have cooled slightly, use a piping bag to fill each donut with the custard until they feel plump and the custard peeks out slightly.

Dust the filled donuts with powdered sugar just before serving. Arrange on a plate and enjoy them warm.