Pre-heat the oven to 350°F. Spray a donut pan with spray oil and set aside.
In a large bowl, combine the flour, cocoa powder, sugar, espresso powder, salt and baking powder.
In a separate medium bowl, mix together the eggs, buttermilk, greek yogurt, vanilla and melted butter.
Mix the wet ingredients into the dry ingredients and stir until just combined.
Spoon the batter into the donut pan *do not fill more than 3/4 full*
Bake for 10 minutes, or until donuts spring back when touched.
Cool in the pan for 5 minutes, then invert onto a wire rack and cool completely.
Dulce de Leche Glaze:
In a medium pot, melt the butter with the sugar and sea salt.
Bring to a boil, and stir in the dulce de leche, milk, corn syrup and vanilla.
Return to boil, stirring frequently to dissolve the dulce de leche. Simmer for 3 minutes, stirring occasionally.
Stir in the powdered sugar until completely dissolved, 3-5 more minutes.
Notes
Dulce de Leche glaze recipe is from Food & WineThere will be left-over Dulce de Leche glaze. Keep in a sealed container in the refrigerator for up to 1 week, and heat gently to use again.