Preheat oven to 350°F. Grease and flour deep 9X13 pan. Can use pan coating make with 1 cup flour, 1 cup oil, 1 cup shortening mixed well; keeps indefinitely in refrigerator; just paint on pans as nessecary. Sift together the sifted flour, cocoa and baking soda and salt, set aside.
Heat the Dr Pepper in a small saucepan over low heat. Add the chocolate chips and stir until melted. Remove from heat, pour into large bowl. With mixer on low add white sugar, brown sugar, butter and vanilla until well blended. In a small bowl beat the eggs and buttermilk until well blended. At lowest speed, slowly add dry mixture and buttermilk mixture alternatively to Dr Pepper mixture. After incorporated beat at medium speed for 2 minutes.
Pour batter into prepared pan; tap on counter genlty to release air bubbles. Bake for 35 to 45 minutes, or until a toothpick comes out clean. Cool slighly in pan for 5 minutes.
1 cup soften butter
4 cups sifted confectioners sugar
1/2 cup chocolate chips
1/4 cup cocoa
1/4 cup Dr Pepper
1-1/2 teaspoons vanilla extract
1/4 teaspoon salt
Heat the Dr Pepper in a small saucepan over low heat. Add the chocolate chips and stir until melted. Remove from heat, stir in remaining ingredients. Cool slightly. Using an electric mixer, beat frosting until fluffy. At this point you can pour onto cake while cake is warm and let frosting soak into cake. This will make your cake have a fudge like consistency. Or you can invert cake onto plate. Whip frosting on high until light and fluffy. Frost cake as usual. The choice is yours, try it both ways!