Out of baking powder? For 1 teaspoon, whisk 1/4 teaspoon baking soda with 1/2 teaspoon cream of tartar just before you use it.
1 tsp baking powder = 1/4 tsp baking soda + 1/2 tsp cream of tartar (mix just before use)
Good for pancakes, muffins and cookies. It starts reacting once it’s wet, so mix and bake without waiting. How much lift you get depends on the recipe and your timing.