Melt chocolate in a microwave safe measuring cup or other glass dish at 20-30 intervals. Stop intervals once chocolate is almost melted and stir until smooth. Set aside to cool for at least 5-10 minutes.
Preheat oven to 350 degree F and grease and flour two 8 or 9 inch round cake pans and line with parchment paper.
Mix the flour, baking soda and salt together and set aside.
Beat butter until soft.
Add brown sugar and eggs and beat with an electric mixer at a high speed for 5 minutes.
Beat in the vanilla extract and melted chocolate.
Alternate adding in dry ingredients with spoonful of the cup of sour cream, beating continually on low speed or stirring with a spoon.
Then stir in boiling water and stir to blended in completely and smooth. (Batter will be thin)
Pour evenly into the two greased pans.
Bake for 40 minutes (8 inch pans) or 35 minutes (9 inch pans) or until a toothpick inserted into center comes out clean.
Cool in pans for 10 minutes then remove and and turn onto wire racks to cool completely.
Frost with this homemade chocolate buttercream frostingUse a quality chocolate bar like GhiradelliUse cake flour or gluten free one-to-one flour like Bob’s Red Mill if desired.Best if flour is weighed to insure that it is not too denseFull fat sour cream is best.Helpful tips:To line pans with parchment paper, place the pan on parchment paper and with a pencil, draw a line around the pan and then cut out with scissors.Pour the one cup of boiling water into the same measuring cup/bowl that you melted the chocolate in and stir to get all the remaining chocolate out.Bake in a bundt pan if preferred