Instructions

For the cake:

1. Pre-heat your oven to 350F (conventional, no fan) and line 3 8″ cake pans with parchment paper
2. Add the flour, baking powder, baking soda, granulated sugar, brown sugar and salt to a bowl and whisk until combined and no lumps remain
3. Add the eggs, oil, buttermilk, sour cream, and vanilla to the same bowl. Use a hand whisk to gently stir until the wet ingredients are combined with the dry and no lumps remain. Do not overmix.
4. Mix the instant coffee with the boiling water in a separate bowl / cup, and pour it into the batter. Very gently fold until a smooth espresso cake batter forms. Then, fold in the mini chocolate chips.
5. Divide the batter evenly between the three lined pans
6. Bake at 350F for 20 min until a toothpick inserted in the middle comes out with light, moist crumbs attached
7. Let the cakes cool in the pans for at least 20 minutes, then carefully turn them out. Cover with cling wrap and chill in the fridge for 30-60 minutes before frosting.

For the filling:

1. Beat together the butter and pistachio butter until smooth. Slowly add in the powdered sugar until well incorporated and fluffy.

For the frosting:

1. Warm a medium-sized saucepan to medium heat and add butter. Once the butter has completely melted, allow it to brown, stirring frequently and gently scraping the bottom of the pan with a spatula. The butter will foam and sizzle as brown specks appear on the bottom of the pan. When the aroma of the pan is nutty and the bottom of the pan is a toasty-brown color remove from heat and let cool completely.
2. Once the butter is completely cooled, beat the butter and sugar together; first on low speed, then increasing as the two ingredients become incorporated. Add the vanilla, salt, and milk, and continue to beat until smooth. If the frosting is still too thick, add more milk, one tablespoon at a time, until the desired consistency is achieved.

Assemble:

1. Put down one layer of cake and add spread out a thin layer of the brown butter frosting on top. Layer on half of the pistachio filling and spread out to nearly the edges. Sprinkle more mini chocolate chips on, if desired.
2. Do the same with the next layer of cake, and then place the top layer. Frost along the outsides with the brown butter frosting.