3 tbsp. butter
1 cup finely chopped onion
1 clove garlic, chopped
1 can (14 oz.) diced tomatoes
1 tsp. celery seeds
1 tsp. salt
1 tsp. black pepper
2 small to medium onions
1 ¼ to 1 1/2 lb. ground beef (80% lean)
Kosher salt and coarsely ground black pepper
About 1 tbsp. canola or peanut oil or other neutral-flavored oil
8 slices American cheese
4 large soft rolls (I like Martin’s Big Marty’s rolls)
Sliced dill pickles
Chopped iceberg lettuce
In a small saucepan with a lid, melt the butter over very low heat. Add the chopped onion and garlic. Cover and cook, stirring occasionally, until the onion is sweet, light golden, and very soft, about 1 hour. (Do not allow the onion to brown.) Add the tomatoes, celery seeds, salt, and pepper. Cover and cook, stirring occasionally, until the tomatoes soften and the sauce thickens, about 3 hours more. Using a blender, purée the sauce. Transfer to squeeze bottles or an airtight container. Refrigerate until cold, about 2 hours. (The sauce can be refrigerated for up to 2 weeks.)
Heat a large cast-iron skillet or griddle over medium-high.
Using a mandoline or the slicing side of a box grater, shave the onions as thinly as possible.
In a bowl, season the beef with salt and pepper; form into 4 equal portions. Roll the meat into balls.
Drizzle the oil in the skillet or over the meat. Place the meat in the skillet, spacing the balls about 3 inches apart; top each with one-quarter of the onions. Using a spatula, press the onions into the meat until flattened into patties. Cook the patties for 3 to 4 minutes, then flip them over. Pressing the patties often with a spatula, cook for 2 minutes. Top each patty with 2 slices of cheese. Cook until the cheese melts, about 2 minutes more.
Build the burgers with the roll bottoms, pickles, lettuce, patties, sauce, and roll tops.