A repost from my old baking blog.

I have several go-to recipes when I need a chocolate cake from scratch. This is my favorite — it’s so easy!

Cooking spray for pans
Cake flour or cocoa powder for dusting
4 ounces (120 g) unsweetened chocolate

1/2 pound (230 g) unsalted butter
2 teaspoons vanilla extract
2 cups (280 g) cake flour
2 cups (400 g) sugar (you can use a little less, about 1 1/2 cups, if you want a less sweet cake)
2 teaspoons cream of tartar
1 teaspoon baking soda
1 teaspoon salt
1 cup milk (I usually use whole, but have tried 2% and 1% and the cake still came out good)
4 eggs

Equipment: Parchment rounds, 8- or 9-inch round cake pans

Preheat oven to 350 degrees F. Spray pans with cooking spray and flour (or use cocoa powder, which I like for chocolate cakes) cake pans. Melt chocolate and butter in a microwave-safe bowl or measuring cup, in 15-30 second intervals, until smooth. (Alternatively, do this in a double boiler or in a heavy-bottomed pan over low heat — watch carefully to make sure chocolate doesn’t burn.) In a bowl, whisk together flour, sugar, cream of tartar, baking soda, and salt. Add chocolate mixture, milk and eggs and beat until smooth. Pour, distributing evenly, into prepared pans, and bake for 25-30 minutes or until cake tester comes out clean and cake starts to pull from the sides of the pan. Cool in pans on racks for 5 minutes before turning out onto racks. The cakes are ready to be frosted at this point, or cool completely and wrap in plastic wrap then foil if freezing for future use. The cakes can also be wrapped and refrigerated for a few days before using.