Patties: In a large bowl add the ground beef, Worcestershire sauce, Dijon mustard, horseradish and lightly mix to combine.
Shape into 3 x 5.5 oz patties (about ¾” thick x 4 ½” diameter). Season with salt and pepper.
Spicy Sauce: Add the mayonnaise, ketchup, and hot sauce into a small bowl. Mix to combine. Cover and refrigerate until ready to use.
Chimichurri: Add the shallots, jalapeños, garlic, red wine vinegar, cilantro, parsley, oregano into a food processor and blitz to combine. Then stream in the oil with the processor on. Cover tightly and set aside.
Cook the Burgers: Before you start cooking the burgers, toast your buns using a toaster, toaster oven, or oven broiler.
Heat a large 12.5” skillet on medium-high. When the skillet is hot, add the beef tallow into the skillet.
Brush one side of the patties with yellow mustard.
When the tallow has melted, add the patties (mustard sided down) into the skillet. Then brush mustard on the other side of the patties. Cook for 4 to 5 minutes per side, until a nice crust is formed.
Add a slice of provolone cheese to each patty, then place a lid on the skillet. Turn down the heat to low and cook covered until the cheese is bubbling, 3 to 5 minutes.
Build the Burgers: Spread a spoonful of the spicy sauce on the bottom bun, then add the lettuce. Add a patty, then spoon chimichurri overtop. (Repeat this step if you are having a double burger.) Add the onions and finish with the top bun.
Optional, spear a pickle using a bamboo skewer, through the top of the burger.
Serve with fresh summer salads, like a Cucumber Salad and/or a Dill Pickle Potato Salad.