Heat a flat-top grill or cast iron pan over very high heat. Form the ground beef into a tight ball and season with salt. Place hamburger ball on grill to sear for 45 seconds, then flatten with a heavy spatula to about ⅓ inch thickness.
Cook for 90 seconds to develop a crust on the first side of the bottom. Flip over and cook on the second side for one minute to develop another crust. Add cheese sauce to the top of the hamburger and top the cheese sauce with a slice of cheese. (This is where it gets good.)
Combine the garlic and melted butter. Brush the inside of bun halves with the mixture and toast on the grill or pan for 3-4 seconds, until golden and crisp. Flip and toast for 3-4 seconds so the outsides are also lightly toasted.
Making the sauce:
Combine ingredients together in a bowl and mix well.
That’s it — you just made Donkey Sauce!
Put it all together
Smear Donkey Sauce on the sliced side of both bun halves.
Layer the base with pickle slices and the burger patty.
Top burger with crispy onion ring (if using), BBQ sauce, sliced onions, tomato and lettuce.