Preheat oven to 350 degrees F (180 degrees C).
Spray the bottom and sides of an 8-inch square cake pan with
Nonstick Cooking Spray (as needed)
. Cut a piece of parchment paper to the dimensions of the cake pan and fit it into the bottom (this is an extra layer of protection against sticking). Set aside.
In a large bowl, beat the
Unsalted Butter (1/3 cup)
Brown Sugar (3/4 cup)
Granulated Sugar (2 Tbsp)
until fluffy. Use a rubber spatula to scrape down the bowl.
Vanilla Extract (1 tsp)
and beat until combined.
Buttermilk (3/4 cup)
and beat again -- mixture will look curdled.
Sift together the
Unsweetened Cocoa Powder (1/2 cup)
All-Purpose Flour (1 cup)
Baking Soda (1/4 tsp)
Baking Powder (1/2 tsp)
Salt (1/2 tsp)
and beat into the butter mixture on low speed until just combined.
Transfer the batter into the prepared pan and use a spatula to spread it out evenly.
Bake for 30-35 minutes until a cake tester comes out clean.
Cool the cake for 5-10 minutes in the pan, then invert it onto a cooling rack and cool cake completely before frosting.
To make the frosting, first, melt the chocolate. Place the
Unsweetened Chocolate (1/3 cup)
in a small microwaveable glass bowl and heat in a microwave oven in short 15-20 second increments until the chocolate has melted into a glossy pool. Don't stir. Cool to room temperature.
In a large bowl, combine the
Powdered Confectioners Sugar (1 1/2 cups)
Unsalted Butter (1/2 cup)
Salt (1/8 tsp)
Heavy Cream (1 Tbsp)
Vanilla Extract (1/2 tsp)
. Beat on medium speed until smooth and creamy.
Add the room temperature chocolate and beat until well combined.
Turn the mixer up to a medium high or high and beat it for a minute more.
Place the cake upside down on your cake stand or platter.
Spoon the frosting into the center of the cake and use an offset spatula to push the frosting out from the center in short little swirls to give it that dreamy icing landscape. You can frost the sides if you like.