Preheat oven to 350°F
Spray 3 9-inch round baking pans with pam, line bottoms with parchment paper, grease again and set aside.
In small bowl combine cocoa and boiling water with a whisk until smooth. Cool.
In medium bowl stir together flour, baking soda and salt.
In a mixer, beat butter and sugar until fluffy.
Add eggs, one at a time and vanilla.
Slowly add the cocoa mix.
Add ⅓ of the flour mix, then the milk. Then ⅓ of flour and the sour cream. Then, add the rest of the flour.
Mix well and divide into the pans.
Bake 20 mins until the toothpick comes out clean.
Cool and pop out of pans. Remove parchment. (Cool and at this point you can freeze)