This is the Cake Mix Doctor's extender formula. Cake Mix Fix - Anne Byrn
1 ½ cups all-purpose flour
1 cup sugar
2 teaspoons baking powder
¼ teaspoon baking soda
Whisk all dry ingredients together and store in a clean mason jar. When you wish to increase a 15.25 ounce cake mix to 18.25 ounces, add three ounces of this mix (6 tablespoons) to your existing cake mix. The recipe provided can be used for yellow or white cake mixes.
For chocolate mixes, substitute 25 percent of the flour with cocoa powder. Store the cake mix add-in in a mason jar to have on hand as needed. The liquid ingredients for the mixes remain the same.