1cupwhole milk(less if you are making it with yoghurt)
And one of the following
2/3cup plain yoghurt (or 1/2 cup Greek yoghurt)
1 3/4tspcream of tartar
Each option will give you 1 cup of buttermilk
Milk + lemon juice
Add 1 tablespoon of lemon juice to a 1 cup measure. Top it up with milk, stir, and let sit for 5-10 minutes. It will start to curdle - that is what you want!
Milk + white vinegar
Same as with lemon juice. Add 1 tablespoon of white vinegar to a 1 cup measure. Top it up with milk, stir, and let sit for 5-10 minutes.
Milk + yoghurt
Plain yoghurt - Mix 2/3 cup plain yoghurt with 1/3 cup milk, stir and use.Greek yoghurt - Mix 1/2 cup Greek yoghurt with 1/2 cup milk, stir and use.
Milk + cream of tartar
Add 1 3/4 teaspoons cream of tartar to a 1 cup measure. Add about a tablespoon of milk and mix together so that there are no lumps left. Add the rest of the milk, up to the top, stir and let sit for 5-10 minutes.