This butter burger is an ode to Wisconsin, on toast. I cook onions in butter, cook my burgers in the buttery drippings and serve with the onions on top.
Grate enough of 1 onion to measure 3 tbsp. with the juice; reserve for the burgers. Quarter and thinly slice the remaining onions. In a large cast-iron skillet, heat the butter over medium. When it foams, add the sliced onions, thyme and bay leaf; season with salt and pepper. Cook, stirring frequently, until caramel in color and very soft, 20 to 30 minutes, adding the stock during the last 5 minutes of cooking. When the stock is absorbed, use a slotted spoon to transfer the onions to a medium bowl. Reserve the skillet with the drippings.
In another medium bowl, season the beef. Mix in the grated onion, the Worcestershire and garlic. Form into 4 patties (thinner in the centers for even cooking).
Reheat the skillet over medium-high. Add the patties and cook 8 minutes, turning occasionally.
Top the patties with the cheese during the last minute or two of cooking, tenting with foil to melt.
Divide the upland cress among 4 slices of toast; top with the buttery burgers, buttery onions and the remaining 4 slices of toast.