- Melt 1½ tablespoons butter in a large sauté pan over medium-low heat. Add the onions, 1/4 teaspoon each, salt and pepper, and allow to cook, stirring occasionally, until they are deep golden brown and caramelized, about 25 minutes. Add a little water if the onions start to brown too quickly. Remove from the pan, and let cool.
- While onions are cooking combine mayonnaise, garlic, lemon juice and remaining 1/4 teaspoon salt and pepper, stirring until well mixed. Refrigerate until ready to use.
- Preheat grill for medium heat and lightly oil the grate.
- Cook patties on the preheated grill until burgers are cooked to your desired degree of doneness, about 3-4 minutes per side for medium-well burgers to an internal temperature of 160°F.
- Place a slice of cheese on each burger, close grill lid and allow cheese to melt. Remove burgers.
- Melt remaining butter in microwave, slice the burger buns and brush inside with butter, and lightly grill until toasted.
- Spread garlic mayonnaise (aioli) onto each burger bun bottom and top with some greens. Place one grilled burger onto each bun, top with caramelized onions and a slice of tomato. Place top of bun on burgers.
- Serving Suggestion: baked sweet potato fries and a side salad
per serving: 770 calories, 53g fat, 17g saturated fat, 125mg cholesterol, 1090mg sodium, 39g carbohydrate, 3g fiber, 4g sugars, 34g protein