Preheat oven to 350 degrees.
Grease and flour two 8-inch, round cake pans. Set aside.
Melt chocolate in a double boiler or in the microwave and cool.
Sift flour, baking soda and salt into a medium bowl and set aside.
Place butter, sugar and eggs in a mixing bowl and mix on high speed until light and fully for approximately 3 minutes.
Add vanilla and cooled, melted chocolate and sour cream.
Mix on medium speed until well incorporated into the butter mixture.
Add flour, baking soda and salt & beat on low for 30 seconds, then on medium for 1 minute. Scrape down the sides at least twice.
Stir in the water until incorporated fully for about 1 minute. The batter will be thin.
Pour the batter into the 2 pans. Gently tap the pans on the counter to release any air bubbles.
Place the pans in the oven. Bake 30-35 minutes or until a toothpick inserted in the middle comes out clean.
Cool the cakes on a cooling rack for 10 minutes.
Turn out onto the racks to cool right-side-up.
Split each layer in half horizontally to have 4 thin layers.
Fill and layer with THE BEST ICING EVER!!