Divide ground beef into 8 portions.
Place muffin liners in muffin tin - sprinkle each cup with salt and pepper.
Shape each portion of beef into a ball and place in lined muffin cup. Season with salt and pepper on top.
Add another liner on top of the meat and push down to form the burger (I skipped this step and just formed the burgers with my hands.)
Heat a nonstick skillet over medium high heat and cook burgers in hot skillet until slightly browned (3 minutes) then flip over and cook another 2-3 minutes until cooked through.
Mix mayonnaise, ketchup, mustard, and relish in a small bowl to make the sauce.
Add burger to slider bun, top with secret sauce as well as any other toppings and enjoy!