Daughters birthday Saturday and making two cakes. How far in advance can I make it? Do I refrigerate it and then warm room temp and re beat?
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Not very far, unfortunately. Frosting should definitely be at room temperature when you frost, but if you try to revive it from a hardened state (from the fridge), it may split. Plus, the time you spend re-beating the frosting would have been roughly equal to making it fresh anyway!
My mom makes buttercream (hers is similar to American buttercream, but added with sweet condensed milk) 1-2 months before, freeze it in container, and when you want to use, bring it to room temp. If it looks good, use it; if it looks a bit floppy, rebeat it again before using. Works every time.
If I'm going to use buttercream frosting within 5 or so days, I make it and just leave it at room temperature. Longer than that, I refrigerate it, let it come to room temperature again, and remix it a little until it's the consistency I want. (Using the paddle attachment, not the whip attachment.) If your buttercream looks like it's separated or curdled looking, try warming a little bit if it int the microwave (start with about a 1/4 cup) until liquid and mixing it back into the rest of your frosting. I've been making cakes professionally for the past 15 years and I swear by this!