1. Preheat oven to 350°.
2. In a bowl, sift together sugar and flour. Add marshmallows.
3. In a saucepan, mix butter, oil, cocoa, and Coca-Cola. Bring to a boil and pour over dry ingredients -- blend well.
4. Dissolve baking soda in buttermilk just before adding to batter, along with eggs and vanilla, mixing well.
5. Pour into a well-greased 9x13 inch pan and bake for 35 to 45 minutes.
6. Remove from oven and frost immediately.
1. In a saucepan, mix butter, cocoa and Coca-Cola. Bring to a boil, remove from heat, and add confectioners' sugar, blending well. Add vanilla and pecans.
2. Spread over hot cake.
3. When cool, cut into squares and serve.
Yield: 15 servings