Preheat oven to 350F. Grease a mini bundt pan with the chocolate grease using a pastry brush and set aside. This batter will fill up 2 of the mini bundt sizes, if you want to make a regular sized bundt cake, simply double the recipe.
In a large mixing bowl, whisk together the butter, cocoa powder, salt, and water until smooth. Add in the flour, sugar, baking soda, and baking powder and whisk until fully combined. Add in the egg and greek yogurt. Whisk until smooth.
Pour the batter into the pan and bake until a toothpick inserted into the center of the cake comes out clean, about 30 to 35 minutes. Let the cake cool in the pan for 15 minutes and then invert onto a rack.
Let cool completely before glazing. While the cake is cooling, make the espresso glaze. Whisk together the powdered sugar and coffee, if the glaze is too thick add some milk. Drizzle the glaze over the cakes. Cut and enjoy!