This is just the type of thing that happens to me all the time! You see we live on a yacht and shops are sometimes not all that easy to get to...and do I love to bake!
This one is easy:
2tsp Cream of Tartar
1 tsp Bicarbonate of Soda
Makes 3 tsp of baking powder.
If you don't have cream of tartar, sorry but you can't make baking powder.
If you have had a the cream of tartar and bicarb for a while add half a tsp of mixed product to 125ml of water and see if it fizzes. If it fizzes your baking powder is active.
This little trick has saved me on more than one occasion and I always have cream of tartar in stock just in case.
