Stir sauce ingredients together until well combined.
For the bun, I butter both sides and toast it until butter melts and edges get a little crispy.
Smother some sauce on bottom bun.
Put on tomato slice.
Place lettuce on top on top of tomato.
Place patty on top of lettuce.
Top the patty with onion and a little more sauce.
Place on the bun top and dig in!
