Melt chocolate in the microwave on low. Allow to cool.
Sift flour, baking soda, and salt; set aside.
In a large bowl, beat the softened butter until soft and fluffy. Add brown sugar and eggs and continue to beat. Add in vanilla and add cooled chocolate and gently fold together.
Stir in the dry ingredients alternately with sour cream, beating well. Stir in boiling water.
Pour the batter into greased and floured 9×13 cake pan or two 9 in. layer pans. Bake for approximately 35 min. (9×13) or 25 min. (9 in. pans) or until done.
Cool cake on wire rack 10 min.
Make the whipped cream frosting:
In a small bowl, whip the cream. Add the cocoa, powdered sugar, and vanilla. Lightly mix until combined. Spread on top of the “cooled” chocolate cake. Slice and serve!