Preheat oven to 350 degrees. Sift all dry ingredients into a bowl and set aside.
Gently beat the eggs with a fork to break up the yolks, then combine with the Greek yogurt, melted butter, vanilla, and bittersweet chocolate. Add the milk and whisk to combine.
Pour wet ingredients into dry and gently stir with a spatula just until combined. If you continue to mix the batter longer than is needed, the donuts will not be as soft!
Lightly grease the donut pan and spoon or pipe batter into molds 1/3 full. Bake for 12-15 minutes, or until a toothpick comes out clean after being inserted.
Let donuts cool in the pan for 5 minutes, then flip onto a cooling rack.
For the Chocolate Glaze
In a medium bowl, combine the melted chocolate chips and milk and either microwave at 30 second increments, or place the bowl over a double boiler until ingredients melt. If you are using a double boiler, stir occasionally to make sure the chocolate doesn’t burn.
Add the milk and whisk until chocolate glaze is smooth.
Dip donuts in the glaze and let them dry on the cooling rack. Sprinkle with chocolate sprinkles or flaked sea salt if desired.