1cupbuttermilkor substitute 1 cup milk + 1 teaspoon vinegar
Preheat oven to 350° F. If using a 13"x9" cake pan, butter pan and set aside. If using paper cake molds (see notes for the 3.5" molds I used) there is no need for butter; simply place the molds on a baking sheet.
In a medium bowl, combine flour, brown sugar, granulated white sugar, and cinnamon. Add oil.
Take 3/4 cup of this mixture and add the chopped nuts; this is the streusel topping. Set aside.
To the mixture without nuts, add buttermilk, egg, baking powder and baking soda. Mix until just well incorporated. Stir in 4 oz each of the raspberries and blackberries, reserving some for the topping. Pour batter into baking pan(s) and sprinkle with streusel topping. Nestle 3 berries on the tops of each cake.
Baking times:20-24 minutes for mini cakes, or until a toothpick inserted in the center comes out clean.35-40 minutes for large 13"x9" cake, or until a toothpick inserted in the center comes out clean.
What size pans to use? The recipe makes eight 3.5" mini cakes, or one 13"x9" rectangle cake.For mini-cakes, I used these 3.5-inch paper molds.Recipe adapted from 3.5-inch paper molds, as seen here on Kitchen Confidante.