Preheat oven to 350°F (177°C). Grease two 9-inch round cake pans, line with parchment paper rounds, then grease the parchment paper.

Whisk the flour, cocoa powder, baking soda, baking powder, espresso powder (if using), and salt together in a large bowl.

In another large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the oil, granulated sugar, brown sugar, eggs, sour cream, and vanilla together until combined.

Add the zucchini and mix to incorporate.

Add the dry ingredients to the batter and beat on medium speed until completely combined. Fold in the chocolate chips.

Pour batter evenly into cake pans. Bake for around 28–32 minutes or until the cakes are baked through.

Set the cakes on a cooling rack and let cool in the pans for 1 hour. After 1 hour, remove the cakes from the pans, discard the parchment rounds, and let the cakes finish cooling directly on the rack.

With a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy, about 2 minutes.

Add confectioners’ sugar, cocoa powder, 3 Tablespoons of cream, salt, and vanilla. Beat on low speed for 30 seconds, then gradually increase to high speed and beat until it’s smooth and creamy.

Assemble and frost: Slice a thin layer off the tops of the cakes to create a flat surface. Place 1 cake layer on your cake stand, cover the top with frosting, top with 2nd cake layer and spread the remaining frosting all over the top and sides. Decorate with chocolate sprinkles or chocolate chips if desired.