recipe adapted from Miette; makes two 6-inch cakes or a couple dozen cupcakes
Prepare two 6-inch cake pans by brushing inside with very soft butter and dusting with cocoa powder. Preheat oven to 375° F.
Put chopped chocolate in small bowl and pour over the boiling water; set aside to melt and cool.
Sift together into bowl: flour, cocoa, baking soda, and baking powder. Sprinkle with the salt and set aside.
Add cooled chocolate and vanilla to the milk and stir to combine.
Using whisk attachment on standing mixer, whisk eggs for a couple minutes on high speed, until foamy. Add the oil and whisk a minute on medium, then gradually add sugar and whisk a couple more minutes. Reduce mixer speed to low, then add the cooled chocolate and milk alternately with the sifted dry ingredients—aim for about four cycles, mixing just until incorporated.
Divide the batter between the prepared pans and bake until tops spring back when lightly touched with the tip of your finger or a tester inserted in the centers comes out clean, about 40–45 minutes.
Cool in pans for 20 minutes, then carefully run a knife or thin metal spatula around the edges of the cakes to loosen them, invert onto cooling racks and remove the pans. Let cool about 20 minutes longer, then either serve, or wrap tightly in plastic wrap and refrigerate until ready to frost and/or decorate—at least 1 hour or for up to 3 days. (You can pop the wrapped cake in a freezer bag and freeze for up to 2 months.)