If a recipe calls for baking powder it is important that it is still fresh enough for the leavening process it was intended to do. We often buy baking powder or baking soda (bicarbonate) and it gets shoved in the back of a cupboard. Who knows how long it's been there. If you are smart you would have put a date on it, but honestly who does that sort of thing?! This is a sure fire way of testing you baking powder before you make a cake that flops:
Add a teaspoon to a cup of water. If it just sits there and doesn't bubble and fizz, it is time to toss that stuff away.
You are welcome for the wonderful tip of the day.