Place a colander in the sink and bring 3 cups of water to a boil in a kettle or on the stovetop. While the water is heating up, cut off the tip end the onion (not the root), and slice in half from root to tip. Peel and then slice thinly into half moons. Place the slices in the colander and pour the boiling water on top.

Add the vinegar, salt and sugar to a medium container or jar with a tight fitting lid, and stir to dissolve. Add the onions, close with the lid, and allow to sit for a minimum of 30 minutes.

While the onions are pickling, allow the ground beef to come to room temperature. (Note: I like to let to meat come to room temperature for approximately 45 minutes, so if you’re pickling the onions for the minimum amount of time, you can remove it from the refrigerator before Step 1.) In a large bowl, toss the ground chuck together with the Worcestershire sauce, minced onions and pepper. Divide the mixture into 6 equal portions, and shape into patties.

If using, spread a thin layer of butter on the inside of each slider bun.

Heat 2 large sauté pans over medium-high heat (Note: the burgers can also be grilled outside). Add approximately 1 tablespoon high heat oil to one pan and add the burgers, cooking in batches if necessary. Add the buns, buttered-side down, to the other pan, cooking in batches if necessary. Cook the burgers for approximately 3 minutes, flip, and cook for an additional 2-3 minutes, until the inside is cooked through but still just slightly pinkish in the middle. During the last minute of cooking, top each burger with cheddar cheese. Cook the buns until they’re golden brown.

Top each burger with a generous portion of picked onions (I also like to add ketchup).