Grate potatoes using the Grate Master System. Into the bowl of grated potatoes, add melted butter, season with salt and pepper then stir to combine.
Place molding ring of the Hamburger Press inside a Hamburger Keeper, then place about ½ cup of grated potato inside the ring and press. Remove the ring, and place the resulting "potato pancake" onto the Silicone Baking Sheet with Rim. Using the same Keeper, repeat until you have 8 potato pancakes evenly spaced on the baking sheet.
Place the oven rack with the filled Silicone Baking Sheet on the lowest level in the oven and bake for 40-45 min.
Season ground beef with salt and pepper and mix to combine. Then evenly divide into 4 equal portions and form into patties using the Hamburger Press.
Cook burgers in a fry pan over medium heat for 2-3 min*. Flip patties, cook for 1-2 min, then add sliced cheese on top, place cover on fry pan and cook for 1 min. Adjust cooking time as needed until you reach desired doneness.
Remove burgers from pan and let rest for 5-10 min. before serving.
At end of baking time or when potatoes are done, remove oven rack with Silicone Baking Sheet and place on heat proof surface. Flip each potato "bun," and spread ketchup on each. Place lettuce on 4 potato buns with ketchup side up. Add burger patties, top with mustard and tomato slices, then place remaining potato buns on top, ketchup side down. Top with arugula if desired. Serve immediately.
*Check internal temperature to find out if your burger is done to your liking! And remember to remove burgers from pan a little before desired temperature, as the internal temperature will continue to rise after cooking.
