I just made the Magnolia Bakery Vanilla Buttercream and I added too much milk or PS. What can I add to thicken my buttercream? I skimmed thru the "Everything you ... about buttercream," but may have overlooked the answer.

Add more PS.

Thanks Alot. I am new to this, so I wasn't sure if more PS would thicken it or liquify it more. Now, if more PS makes it too sweet, do I add salt or what?

it shouldnt make it too much sweeter, because your not adding alot, try adding PS to a little bit first before you do the whole batch.