Prepare the Dough: Combine active dry yeast and warm water in a small bowl. Let it sit for about 5 minutes until foamy. In a stand mixer, mix warm milk and softened unsalted butter until smooth. Gradually add the yeast mixture, granulated sugar, eggs, fine sea salt, and all-purpose flour. Mix on low speed until a soft dough forms.

First Rise: Transfer the dough to a greased bowl, cover with plastic wrap or a damp cloth, and let it rise in a warm environment until it triples in size, approximately 1 hour.

Knead and Shape: Punch down the risen dough gently, then turn it onto a floured surface and knead briefly. Roll out to about ½ inch thick, and use a round cutter to cut into circles.

Second Rise: Place cut doughnuts on a greased baking sheet, cover with a kitchen towel, and let them rise for another 45 minutes.

Fry Donuts: Heat frying oil in a heavy pot to 360°F. Add risen doughnuts in batches, frying each side for 1-2 minutes until golden brown.

Make Filling: In a medium saucepan, whisk together egg yolks, sugar, and cornstarch. Heat remaining milk until simmering and whisk into yolk mixture. Cook on medium until thickened, stirring constantly. Remove from heat, add butter, vanilla, and salt, then chill.

Fill Donuts: Use a pastry bag fitted with a small round tip to fill each doughnut with the cooled pastry cream.

Prepare Glaze: Heat heavy cream until simmering, pour over chocolate chips, let sit for a minute, then whisk until smooth.

Glaze Donuts: Dip filled doughnuts into the chocolate glaze, allowing excess to drip off. Place on a wire rack to set.