I love to use real butter in my baking, and when I shop I usually buy one salted butter, and one unsalted. But, as unsalted butter isn't as common in ingredients as salted butter, I'm left with a bunch of sticks of unsalted butter cluttering up my freezer. How much salt do I need to add to make up the difference?
Victoria, we are going to answer your question in a roundabout way. Unsalted butter really ought to be the staple of your kitchen baking — not the other way around. Unsalted butter is much to be preferred in baking, since it is usually slightly fresher and sweeter, and it lets you add the exact amount of salt you want in your recipe, instead of trusting the butter's salt content.
So our advice would actually be to use the unsalted butter in your cooking and baking, and to reserve your salted butter for the table only.
Readers, any more thoughts?