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Preheat oven to 350°F. Grease and line two 8-inch round cake pans with parchment paper.
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In a large mixing bowl, sift together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.
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In another bowl, whisk together the eggs, buttermilk, vegetable oil, and vanilla extract; Stir in the hot espresso water.
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Slowly add the wet ingredients to the dry ingredients, mixing until smooth and combined. Divide the batter evenly between the prepared pans. Bake for 28-32 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.
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For the chocolate filling, heat the heavy cream in a small saucepan until just below boiling. Pour over the chocolate chips in a heatproof bowl and let sit for 2 minutes. Stir until smooth and let cool slightly.
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For the frosting, beat the butter and cocoa powder together in a large bowl until creamy. Gradually add the powdered sugar, alternating with the heavy cream, until smooth and spreadable. Stir in the vanilla extract.
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Place one cake layer on a serving plate. (I like to pipe an icing dam around the edge of the cake layer to keep the ganache in place.) Spread the ganache over the layer evenly, allowing it to set for 5 to 10 minutes. Spread the buttercream (about 1/3 cup)on top of the ganache, smoothing it out evenly.
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Add the second cake layer on top, then frost the entire cake with the buttercream frosting.
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Garnish with mini chocolate chips.