Make the Cream
- Heat the half and half, milk, and vanilla extract. Use a medium saucepan set over medium low heat, then heat the liquid, stirring frequently, until it starts simmering.
- Make the egg mixture. In a separate mixing bowl, whisk together the egg yolks, sugar, and cornstarch.
- Combine. Gradually pour the egg mixture into the hot milk, whisking constantly. Cook over medium-low heat, stirring constantly, until thickened. Make sure you don’t stop whisking or your eggs will scramble instead of transforming into a rich and creamy base.
- Add butter. Remove the mixture from the heat and add the butter, 1 tablespoon at a time, continuing to whisk until melted and smooth.
- Cool and Chill. Let the cream cool to room temperature, then place a piece of plastic wrap on the surface of the cream. Chill in the refrigerator for 1 hour.
Make the Donut Dough
- Combine dry ingredients. In a large mixing bowl, combine 3 ½ cups of flour, sugar, yeast, and salt.
- Mix wet ingredients. In a separate mixing bowl, whisk together the water, eggs, melted butter, and vanilla extract.
- Combine. Gradually add the wet ingredients to the dry ingredients, mixing until a dough forms. Add the remaining ½ cup flour as needed to form a soft, elastic dough.
- Rise. Cover the bowl with plastic wrap and let the dough rise for 1 hour in a warm, draft-free place until doubled in size.
Shape and Fry the Bismark Donuts
- Roll it out. Once the dough has doubled in size, roll it out on a floured surface to ½ -¾ inch thickness.
- Shape the donuts. Using a donut cutter, cut out circles of dough and place them on a baking sheet covered with pieces of parchment paper to rise for another hour.
- Heat the oil. Heat vegetable oil (about 3 inches deep) in a medium-sized heavy-bottomed saucepan to 350°F.
- Prep your tools. While the oil heats, line a baking sheet with paper towel and set aside.
- Cook. Fry the donuts until golden brown, turning once. Remove the donuts from the oil and let them cool on the paper towel-lined tray.
Fill the Donuts and Add the Chocolate Glaze
- Fill with cream. Using a piping bag with a small round tip, fill the donuts with the prepared cream.
- Make the glaze. Heat the whipping cream in a small saucepan until simmering. Add the chopped dark chocolate and stir until melted and smooth.
- Glaze the donuts. Dip the tops of the cooled donuts into the chocolate glaze and let them set.