Preheat oven to 350º F. Make sure racks are in the center of the oven. Prepare two 9-inch cake pans by buttering and lightly flouring or, as I did, buttering the whole pan and lining the bottom with parchment.

Add flour, sugar, cocoa, baking powder, baking soda, salt and espresso powder to the bowl of a stand mixer. Using the paddle attachment, stir flour mixture until combined well.

Bring the water to a boil

Mix milk, vegetable oil, eggs, and vanilla in a separate bowl and add to flour mixture and mix on medium speed until well combined. Reduce speed and carefully add boiling water to the cake batter until well combined. It will be thin.

Distribute cake batter evenly between the two prepared cake pans. Bake for 30-35 minutes, until a toothpick or cake tester inserted in the center of the chocolate cake comes out clean.

Remove from the oven and allow to cool for about 10 minutes. Then gently slide a knife around the edges and remove from the pan, peel off the parchment (if you used it) and cool completely on a rack.

NOTE: I have successfully made this cake in three 8-inch pans (prepared as above), baked for 25-30 minutes.

After the cake is completely cool, make the frosting.

To prepare frosting, in the bowl of a stand mixer fitted with the paddle attachment, beat butter on medium speed until very pale and creamy, about 5 minutes. Scrape down the sides of the bowl. On low speed, add the sifted powdered sugar and cocoa powder and mix to combine. Add sour cream, hot water, vanilla and salt and mix on low speed until the liquid is incorporated, scraping down the sides of the bowl as needed. It may look slightly curdled at this point, but don’t worry. Increase speed to medium-high and beat until smooth, another 2-3 minutes. Add lukewarm chocolate and mix until smooth and glossy.

At this point you have about 30 minutes at cool room temperature (longer in the summer) to work with the frosting before it begins to harden (this frosting doesn’t do particularly well when made ahead of time).

To assemble, level your cake layers first if necessary (if there is any sort of domed top, you want to trim that off with a serrated knife). Place one layer, bottom side up, on a cake stand or serving platter (on a piece of parchment if you will need to move it). Spread about 1 cup of frosting in an even layer, then place second layer on top, flat side up, pressing gently to adhere.

Cover the entire cake with a thin layer of buttercream using an offset spatula. This “crumb coat” will seal in the cake crumbs and make the final layer of frosting easier. My final coat was applied with a large star tip in a swirled pattern.

Serve immediately or cover with a cake dome. It will stay nice for a day. After that, refrigerate until serving. Do not leave the frosted cake in direct sunlight. It’s not pretty.