Heat oven to 350°F. Coat two 8 x 2-in. round cake pans with nonstick spray. Line bottoms with wax paper; spray the paper. Dust with flour.

In a large bowl, whisk together flour, cocoa, granulated and brown sugars, baking soda, baking powder and salt. In a large measuring cup or bowl, whisk together milk, oil, eggs and vanilla. Add the milk mixture to the flour mixture and mix until fully incorporated.

Add the boiling water to the batter and mix well to combine (the batter will be thin). Divide the batter between the prepared pans and bake until a wooden pick inserted in the center comes out clean, 35 to 40 minutes. Let cool for 10 minutes in the pan before transferring to a wire rack to cool completely.

Meanwhile, using an electric mixer, beat the heavy cream, sour cream and confectioners’ sugar in a large bowl until stiff peaks form. Place one of the cakes on a platter and spread 1 cup frosting over the top. Top with the remaining cake and frost with the remaining icing. Gently pat the coconut all over the cake. Serve immediately or refrigerate, up to 1 day.