A couple leftover brownies, some unused ice cream mix, a little peanut butter…sounds like peanut butter brownie ice cream to me. For all those who are having trouble with icy, crystal-filled ice cream this summer, try peanut butter. Commercial peanut butter has all kinds of emulsifiers in it to keep it from separating, and those same emulsifiers will go on to keep water crystals from forming in your ice cream. Plus it tastes good. Really good.