1. Preheat oven to 350 degrees.

2. Prep 3 9-inch round cake pans by greasing the inside of each pan, adding a circle of parchment paper to the bottom (to prevent sticking), and then flouring the sides of the pan.

3. In a large mixing bowl, cream the butter and brown sugar together until light and fluffy. Add eggs, one at a time, beating well after each addition. Stir in vanilla.

4. Sift the flour, cocoa powder, baking soda, and salt into another large mixing bowl. Whisk to combine. Add the wet mixture and sour cream to the dry ingredients and beat with an electric mixer just until well blended. Add the boiling water then stir until combined.

5. Pour the batter evenly into the three prepared cake pans. Bake at 350 for 30-35 minutes until a toothpick or cake tester is inserted and comes out clean. Set the cakes aside to cool.

6. Microwave the butter in a microwave safe bowl just until melted. Stir in the semi sweet and unsweetened chocolate. Microwave in 30 second intervals, stirring between each interval, until the chocolate is melted.

7. In a large mixing bowl, combine the powdered sugar, sour cream, and vanilla. Add the chocolate mixture and beat until smooth.

8. Place the first cake layer onto a plate or serving platter. Cut strips of waxed paper and place them just slightly under the edges of the cake to cover the platter and protect it from the frosting. Frost the top of the cake, add the second layer, frost the top of the second layer, then add the third layer. Use the remaining frosting to frost the top and sides of the cake. Remove the waxed paper.

Leftover cake should be refrigerated.