Heat a large, wide skillet or sauteuse over medium heat. A vessel with a lid will speed things along, but you can also use a smooth griddle pan. Butter the insides of the slider buns and place butter side down in the pan. Heat until browned. (You might have to do this in batches if your pan is not large enough.) Remove the buns and set aside.

Add about a tablespoon of olive oil to the pan and heat until shimmering. Add the onions slices and stir to coat with the oil. Lay the sausage patties among the onions and cook for 5 minutes on one side. Move the onions around with a spatula so they don't burn in place. Flip the patties and cook for another 4 minutes.

Scoop some of the onions on top of each patty.

Slice (or fold and tear) each cheese slice into four equal pieces. Place one or two cheese quarters on top of the onions. If you have a lid, place the lid on the pan - the steam will help melt the cheese.

While the cheese melts, spread your condiments on the buns. When the cheese is nice and gooey, use a spatula to carefully lift each cheese-onion patty onto a bottom bun. Lay pickle slices into the melty cheese, and then top with the other bun half.