Preheat the oven to 350-degrees.
Grease or spray two 9-inch cake pans and line the bottoms with rounds of parchment paper.
Chop the chocolate and melt it in the microwave or in a double boiler, being careful not to burn it. Set aside.
- Chop the chocolate and melt it in the microwave or in a double boiler, being careful not to burn it. Set aside.
- Sift the cocoa, flour, baking soda, baking powder and salt together in a medium bowl.
- Combine the sugar and butter in the bowl of a stand mixer and beat on medium speed for 5 to 6 minutes. Scrape the bowl and continue beating until the mixture is light and fluffy.
- Add the eggs, one at a time, scraping the bowl after each addition. The batter may look curdled at this point, which is fine.
- Add the melted, cooled chocolate and vanilla and mix on medium speed for 30 seconds.
- With the mixer on low, add the dry ingredients and the milk in several alternating additions, mixing for about 30 seconds after each.
- Remove the bowl from the mixer and use a spatula to make sure the batter is fully blended.
- Pour the batter into the prepared pans.
- Bake until the cakes spring back in the center when lightly pressed, or a tester inserted in the center comes out clean, 25–30 minutes.
- Cool the cakes on a wire rack for 10 minutes. Remove them from the pans and cool completely.
- Fill and frost as desired.