Add all burger sauce ingredients to a bowl and whisk to combine. Refrigerate until ready to use; can be made 3 days in advance. Mix the salt and pepper in a bowl and distribute evenly over the top and bottom of the ground beef. Divide and roll the beef into 2 1/2-ounce balls, handling as little as possible so the meat stays tender. Place on a plate and refrigerate until your cooking surface is preheated. Turn your flat top or skillet onto high heat, ungreased, and allow it to get very hot. Place each ball on the hot surface and set a 6-inch tortilla on top. Use a smashing tool to press down very firmly, smashing the meat until it is as thin as it goes. Let cook for 1 minute, then press down again to render some fat. Let cook undisturbed for 2 to 3 minutes. Use a stiff steel spatula to check that the beef is browned and crispy underneath; if not, increase the heat. Once crisp, flip the tacos onto their tortilla side and cook another 2 minutes so the tortilla crisps. Top with cheese, which will melt as the tortilla finishes. Remove, add burger sauce and toppings, then enjoy!