Combine the flour, yeast, sugar and salt in a bowl. Add the milk, vanilla, egg yolks and butter. Stir until all the ingredients are well combined and the dough starts to come together. Transfer the dough to a floured surface and knead by hand for 2 minutes. Shape the dough into a ball and transfer it to a large oiled bowl. Cover the bowl with a towel and let the dough rise in a warm place for 1 to 1½ hours, until the dough has doubled in size.

When the dough has risen, punch it down and roll it into a 24-inch long log. Cut the dough into 24 pieces. Push a peanut butter cup into the center of each piece of dough, pinch the dough shut and roll it into a ball. Place the dough balls on a cookie sheet and let them rise in a warm place for 30 minutes.

Pre-heat the air fryer to 400°F.

Spray or brush the dough balls lightly with vegetable oil. Air-fry eight at a time, at 400ºF for 4 minutes, turning them over halfway through the cooking process.

While the doughnuts are air frying, prepare the topping. Place the chocolate chips and milk in a microwave safe bowl. Microwave on high for 1 minute. Stir and microwave for an additional 30 seconds if necessary to get all the chips to melt. Stir until the chips are melted and smooth.

Dip the top half of the doughnut holes into the melted chocolate. Let them set up for just a few minutes while you make the peanut butter topping to drizzle on top. Place the peanut butter and milk into a microwave safe bowl. Microwave for 30 seconds. Add the powdered sugar and stir until smooth. Place the peanut butter mixture in a zip lock bag and cut the tip of one corner off to make a small hole. Drizzle thin lines of peanut butter over the chocolate layer on doughnut holes.

Place them on a rack to set up for just a few minutes and watch them disappear.