Baking Powder or Self Raising Flour?

I don't buy self raising flour - I buy plain flour and then use baking powder if a recipe calls for self raising.

If a dried product, (in your example baking powder or as in a thread earlier this week ground ginger) is that long out of date, I wouldn't have used it anyway. If it's only a month, then yes - but if your product is now out of date by *years* .... best bin it and start again.

Basically, baking powder is a raising agent. When the quantities of baking powder to plain flour are given in a recipe it can vary depending on the type of recipe you are making.
For example: generally, for every 8oz of plain flour you would use 4 tsps of baking powder and this would then be "self raising flour".
However, if you were making a sponge cake with plain flour, you would use 3 tsp per 8oz flour; a fruit cake would need only 1tsp per 8oz plain flour

I used to do as Queenie, buy plain flour and add baking powder to make self raising. But since we're about money saving, it's cheaper to buy self raising! If you lookin old (70s and before) cook books, there are usually tables of how much baking powder to how much flour. Generally, the lighter the cake (sponge lighter than scones lighter than fruit cake), the more baking powder.

I have seen recipes that call for self raising flour AND baking powder (I've turned the page and moved on!) but I think SR flour would be fine for brownies.