Preheat your oven to 350°F/175°C. Butter a bundtlette pan (I'm using the Nordicware one) and then sprinkle over cocoa powder. Make sure every nook and cranny is greased and has a thin layer of cocoa powder! This will stop the cake from sticking.
Combine the flour, cocoa powder, sugar, baking powder, baking soda, and salt in a large bowl with a whisk.
6 tablespoons Dutch cocoa powder, ¾ cup + 2 tablespoons granulated sugar, ¼ teaspoon kosher salt, 1 cup all-purpose flour, 1 teaspoon baking soda, ½ teaspoon baking powder
In a medium bowl, whisk together the buttermilk, sour cream, oil, egg, and vanilla extract.
¼ teaspoon vanilla extract, 1 large egg, 2 tablespoons buttermilk, ½ cup sour cream, ¼ cup vegetable oil
Slowly pour the wet ingredients into the dry and mix until just combined.
In a mug or bowl, whisk the espresso powder with the hot water. Pour this hot coffee into the cake batter and whisk until smooth.
½ cup very hot water, ½ teaspoon espresso powder
Pour the batter into the prepared pan, filling each bundtlette so it's ⅔ full. I used a large cookie scoop for this and each bundtlette got 2.5 scoops of batter!
Bake in the preheated oven for 20-25 minutes, a toothpick inserted into one of the cakes should come out clean.
Let the bundt cakes cool in the pan for 10 minutes (set a timer!). I like to use a small rubber spatula to gently edge the cakes away from the sides, to make sure it isn't sticking. I then use oven gloves to give the pan a shake to make sure nothing is stuck to the sides!
Place a wire cooling rack on top of the pan and quickly invert the pan. Gently lift the bundt cake pan off and let the cakes cool completely on a wire cooling rack.
To make the glaze, whisk all of the ingredients together until smooth. Drizzle over the cooled bundt cakes. If you find your glaze is too thick, you can add heavy cream a tablespoon at a time. If the espresso glaze is too thin, add powdered sugar a tablespoon at a time.
1 tablespoon freshly brewed coffee, ½ cup confectioner's sugar, pinch kosher salt, 2-3 tablespoons heavy cream
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I have provided a conversion to US cups, but please note that I haven't tested the recipe with this method. Ingredients: I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients before you start baking.Salt: If you don't have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt. Please note, I'm using Diamond Crystal kosher salt and not Morton salt, which is too salty! Storage: Store the cakes in the fridge for 3-4 days. I recommend letting it come to room temperature before enjoying! Bundt Pan: I'm using the Nordicware Bundtlette pan!