makes two round cake layers 6 to 9-inches; adapted from Flo Braker's chocolate cakes
Preheat oven to 365°F. Spray inside bottom and edges of two round cake pans with cooking spray and line bottom with a circle of parchment. (If making cupcakes, insert paper liners into the pan.)
Melt the chocolate in a double boiler. Improvise by placing the chocolate in a small metal bowl and float this bowl in a larger pan filled with an inch of water set over medium heat on the stovetop. You want the water to be hot enough to melt the chocolate, but not splashing up and over the edge into the chocolate. Stir occasionally until smooth then remove chocolate bowl from water bath and set aside.
Cream the butter in the bowl of a stand mixer for a couple minutes. Add the sugar and beat for 4 minutes, until lightened in color and fluffy in texture. Add the eggs and beat for 3 more minutes. Mix in the melted chocolate.
In a 4-cup glass measuring cup or bowl, mix together the sour cream, water, and vanilla and set aside. In a bowl, whisk together the flour, baking soda, and salt. Add the flour to the chocolate mixture in three parts, alternating with the sour cream/water/vanilla. Mix just until blended and pour into prepared pans.
Bake until center springs back when you gently touch it with your finger and a toothpick inserted into the centers comes out clean, about 45–50 minutes for 6-inch pans. Larger diameter pans will cook faster, start checking at 35–40 minutes for 9-inch pans. Cupcakes will cook quite fast, start checking for doneness at 10 minutes. Transfer pans to racks to cool for 10 minutes. Run a butter knife around the edges of the pans, then invert each onto a rack and remove the pans. Let cool completely before frosting.