lavender essential oil--sparingly applied to the burn. Helps heal with no blister, no matter how bad the burn

also, I'd be wary of mustard. Mustard gas is used as chemical warfare because it burns! the same mustard that gets made into a condiment.

I run cold water over a burn for at least 5 minutes. Once the skin heats up, it keeps cooking unless you cool it down. My grandfather was a firefighter and first responder. He rolls his eyes at all the old wives' tales and ALWAYS treats small first degree burns immediately with running cold water to cool the skin. You should always seek medical treatment for large burns or 2nd and 3rd degree burns.