How to make baking powder in less than a minute.
Mix the baking soda and cream of tartar in a small bowl.
Use immediately.
Note that if your recipe includes yogurt, kefir, buttermilk, lemon juice or vinegar, there is no need to mix up baking powder. Just use baking soda alone and the acidity already included in the recipe will activate it to provide the desired dough leavening effect with no cream of tartar.