“I Want Chocolate Cake” Cake

 

6 tablespoons (85 grams) unsalted butter, at room temperature

3/4 cup (145 grams) firmly packed dark brown sugar

2 tablespoons (25 grams) granulated sugar

1 large egg

1 large egg yolk

3/4 cup (175 ml) buttermilk (see Notes for other options)

1 teaspoon (5 ml) vanilla extract

1/2 cup (41 grams) Dutch cocoa powder

1 cup (125 grams) all-purpose flour

1/4 teaspoon baking soda

1/2 teaspoon baking powder

1/2 teaspoon table or fine sea salt

 

2 ounces (55 grams) unsweetened chocolate, melted and cooled

1 1/2 cups (180 grams) powdered sugar (sifted if lumpy)

1/2 cup (4 ounces or 115 grams) unsalted butter, at room temperature

Pinch of fine sea salt (optional)

1 tablespoons cream or whole milk

1/2 teaspoon vanilla extract

 

Make the cake: Heat oven to 350°F (175°c). Line the bottom of an 8-inch square cake pan with parchment paper, and either butter the parchment and exposed sides of the pan, or spray the interior with a nonstick spray. In a large bowl, use a hand or stand mixer to beat the butter and sugars until fluffy; scrape down bowl. Add the egg, yolk and vanilla and beat until combined, then the buttermilk and mix again. Scrape the bowl down well and don’t worry if the batter looks uneven. Place your flour, cocoa, baking soda, baking powder and salt in a sifter (I find this step necessary because my cocoa is very lumpy) and shake it over the batter bowl. Stir on low until just combined; scrape down bowl a final time. Scoop batter into prepared pan and smooth flat. Bake for 18 to 22 minutes (updated, based on feedback) 25 to 35 minutes, until a toothpick inserted into the center comes out clean. Let cool for 5 to 10 minutes in cake pan on cooling rack, then flip out onto rack or serving plate to completely finish cooling before frosting. Speed this up by placing it outside for 10 minutes (thanks, winter!).  Make the frosting: Place frosting ingredients in a food processor and run machine to mix. Scrape down bowl then process for another 1 to 2 minutes (updated based on feedback) just until smooth and somewhat fluffed. [Don’t have a food processor? Beat butter, powdered sugar and salt, if using, in a large bowl with an electric mixer until fluffy. Pour in chocolate, milk and vanilla, beat until combined, then one more minute to whip it further.] Scoop the frosting onto the cooled chocolate cake and swirl it around. Finish with rainbow sprinkles; don’t even fight it. Cut into squares and prepare for your family/roommates to completely freak out when they spy it on the counter. (But only share if they offer to do dishes.) Cake keeps at room temperature for a day or two, or in the fridge up to a week, or so I’ve heard but never tested out. Notes: Red wine chocolate cake, mocha chocolate cake: You could replace the buttermilk in full with yogurt or sour cream thinned with a little milk or water, with red wine or replace 1/2 cup of it with strong coffee. (Keep 1/4 cup buttermilk so you’ll have an acidic ingredient to wake up the baking soda.)