Step 1

Preheat the oven to 350 F.

Step 2

Prepare a 9-inch round cake pan by spraying it with nonstick spray and lining it with parchment paper.

Step 3

In a large bowl, whisk together the flour, sugar, cocoa, baking powder, baking soda, and salt.

Step 4

Whisk in the eggs, sour cream, vanilla, and oil.

Step 5

Whisk in hot tap water, ¼ cup at a time, until the batter is thick and ribbons, about ½ cup total.

Step 6

Transfer the batter to the prepared pan.

Step 7

Bake until the top springs back when lightly pressed, about 40 minutes.

Step 8

Let cool fully before frosting.

Step 9

To make the frosting, in a stand mixer beat the butter and powdered sugar until fluffy.

Step 10

Add cocoa powder, instant espresso, and heavy cream, and continue to beat until fully incorporated.

Step 11

Slowly drizzle in melted chocolate with the mixer running.

Step 12

Spread the frosting on the cooled chocolate cake.

Step 13

Slice and serve the chocolate cake.