Double acting.
Ingredients: Sodium acid pyrophosphate, sodium bicarbonate, corn starch, monocalcium phosphate

Baking Powder Biscuits: 2 cups all-purpose flour,1 tbsp baking powder, 1/2 tsp salt, 1/4 cup shortening, 1 cup milk.
Preheat oven to 450 degrees F (230 degrees C). Lightly grease a baking sheet. In a bowl mix the flour, baking powder, and salt. Cut in the shortening until the mixture has only pea sized lumps. Add milk and mix until dry mixture is absorbed. Drop dough by heaping spoonfuls onto the prepared baking sheet. Bake for 12 to 15 min in the preheated oven, until golden brown.