Mix and set aside:
3 1/2 c flour
2 c sugar
1/2 t salt
1 t baking soda
1 1/2 c miniature marshmallows
1/2 c chopped walnuts or pecans (or to taste)
Beat and set aside:
1 t vanilla
1 c buttermilk (or substitute; see below)
Bring to a boil:
1/2 c butter or margarine (or 1 stick or 1/4 pound butter or margarine )
1/2 c cooking oil ("very light" olive oil; "virgin" & "extra virgin" are too strong)
1/2 c cocoa powder
1 c Coca-Cola
Pour boiled mixture over dry mixture. Add buttermilk mixture. Add egg mixture. Mix well.
Spray Pam in a 13"x9" pan. Bake at 350 for 40 minutes or until toothpick comes out pretty clean. Don't over-bake. It's easy to do this with chocolate desserts.
Mix this after you take the cake from the oven, and it has cooled about 10-15 minutes. You want some residual heat in the cake to help the frosting (which is thick) spread.
Bring to a boil:
1/2 butter or margarine
1/4 c cocoa powder
1/4 c + 2 T Coca-Cola (6 T)
Add 1 t vanilla.
Pour mixture over a 16-oz. box powdered sugar (about 3 3/4 or 4 c). Thin with leftover Coke or thicken as needed. Pour over warm cake, spreading with moderate quickness. You want it spread before it stiffens. The recipe make plenty for the corners!!
I don't know about you, but I don't have fresh buttermilk hanging around. I often have powdered buttermilk on hand for bread-making, but if I don't have that, I substitute whole milk + a souring agent (acid, such as vinegar, lemon juice, or tartaric acid). If I don't have whole milk, I use whatever I have (including powerdered milk).
Buttermilk substitutes (for 1/2 c needed above): (1) 1/2 T (or scant 2 t) vinegar + whole milk to make 1/2 c fluid; (2) 3/4 t cream of tartar + 1/2 c whole milk; (3) 1/4 c plain yogurt + 1/4 c whole milk + 1/4 t vinegar. Let stand 5 minutes before use.