In a bowl, mix all the ingredients for the special sauce then place in the fridge until ready to use.
Heat your grill at high heat (around 400F) for direct cooking.
Add a cast iron skillet or plancha over the flames to heat and add some sliced bacon to the cold skillet.
Cook the bacon till crispy, then pull off and mop up any excess bacon fat in the skillet.
Grab a handful of ground beef (around 1/4 lbs… ish) and gently roll it into a ball. Repeat this for 6-8 balls or until you’re out of meat.
Get your skillet ripping hot (so it's gently smoking).
Add a burger ball to the skillet. Place a piece of parchment over one ball and then firmly press with the spatula until the burger is “smashed” on the skillet.
Season the patty with salt, pepper and garlic. Let cook for another 1-1.5 minutes.
Before flipping, drizzle some yellow mustard on the unflipped patty.
Carefully flip the burger patty over and then season the new side.
Top with a slice of cheese and let melt for 1-2 minutes. Once melted, pull off and rest.
Repeat for the rest of your patties.
Build your patty melt with an upside down bottom butter bun, slice of cheese, special sauce, double patties, caramelized onions, more special sauce, bacon and the top bun on upside down.
Add the patty melts to the skillet and toast the buns. Once golden brown, serve and enjoy!