Sliders are a small version of a hamburger. A little trick helps you to get them all the same size so they cook evenly and look very professional. Do a couple of tests to determine your perfect degree of doneness and cook all the burgers the same amount of time.
Place ground beef onto a work surface; divide into 8 equal-size pieces using a knife or pastry cutter. Line 8 muffin cups with paper liners.
Sprinkle bottoms of paper liners with salt and black pepper. Form each piece of burger into a rough ball and place into a muffin cup. Season tops with salt and pepper.
Place a second paper liner on top of each piece of meat and gently press it down to shape the mini burger into a round, flat shape. Pull off the paper tops and remove burgers from the muffin cups; remove bottom paper liners from burgers.
Heat a large nonstick skillet over medium-high heat. Cook burgers in the hot skillet until they have a browned crust and are slightly pink in the middle, about 3 minutes per side. Flip burgers and cook 3 minutes on other side. Remove burgers to a plate to rest for 2 minutes.
Mix mayonnaise, ketchup, mustard, and pickle relish in a bowl; spoon a dollop onto each bun. Place burgers onto buns, season with more black pepper, and top with a tomato slice. Close buns and serve.
Per Serving: 214 calories; protein 11.7g; carbohydrates 160.2g; fat 10.9g; cholesterol 35.7mg; sodium 155.4mg.