My mom has been making these for as long as I can remember. I had a few birthdays where I asked for these instead of a regular birthday cake.
These are nothing like brownies from a box, so if you are used to the typical "thick and fudgy" you're looking in the wrong place.
Buttermilk brownies are light, fluffy, cakey, but still plenty rich and decadent. I happen to like mine without nuts, and with a thin layer of frosting. I suppose people that like nuts could add some walnuts or pecans, but I have no idea how much you would want to add. I'll throw out a guess of 1/2 to 1 cup of nuts in the brownie mix.
Another adjustment would be to the frosting. I happen to like it thinner and more like doughnut glaze, just how I have it written out below. But if you like thicker, fluffier frosting, you could just add more powdered sugar. An extra cup works well with the amounts of liquids. However, when you make the frosting with more sugar, it's not as pretty and shiny.
2 cups all purpose flour
2 cups sugar
4 Tablespoons cocoa powder
1 cup cold water
1 stick butter or margarine
1/2 cup vegetable oil
1/2 cup buttermilk
1 teaspoon baking soda
1. Sift together flour, sugar, and cocoa powder. Set aside.
2. In a saucepan, bring water, butter, and oil to a boil.
3. Pour boiling liquid over sifted dry ingredients and beat until creamy.
4. Add buttermilk, baking soda, and eggs. Beat thoroughly.
5. Bake in a large jelly roll pan (about 9x13 or 11x15) for 18-25 minutes at 350 degrees. Check that they are done with a toothpick.
6. Frost while still warm.
1/2 cup butter
1/3 cup buttermilk
1/4 cup cocoa powder
1 small box powdered sugar, sifted (about 3 1/2 cups)
1 teaspoon vanilla extract
1. Bring butter, buttermilk, and cocoa to a boil in a small saucepan.
2. Add powdered sugar and vanilla, then beat until smooth.
3. Frost the brownies while warm so the frosting sort of melts into them and makes a nice glaze.