Cheeseburgers are a classic, a perennial particularly in evidence at grilling time. But being a classic lends itself to personal variations, with much possible finessing of details.

The purist can always revert to the original. Here’s one of the easiest of variations: The burger is grilled, topped with Swiss cheese, lavished with grilled onions, a touch of Dijon-style mustard and mayo. Lettuce and tomato, of course.

Cheeseburgers With Grilled Onion

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1 1/2 pounds ground beef
4 slices sweet onion ( 1/2-inch thick)
Vegetable oil
8 slices (1 ounce each) Swiss cheese
1/4 cup mayonnaise
1 tablespoon Dijon-style mustard
4 crusty rolls, split, toasted
Romaine lettuce leaves
Tomato slices

Lightly shape ground beef into four 3/4-inch-thick patties. Brush onion slices with oil. Place patties in center of grid over medium, ash-covered coals; arrange onion slices around patties. Grill, uncovered, 13 to 15 minutes to medium (160 degrees) doneness, or until centers are no longer pink and juices show no pink color. Grill onions until tender, turning occasionally.

Season patties with salt and pepper after turning, as desired.

About 1 minute before patties are done, top each with 2 cheese slices. Combine mayonnaise and mustard; spread on top halves of rolls. Serve burgers and onion slices in rolls with lettuce and tomato. Makes 4 servings.

Nutrition information per serving: 845 calories, 55 grams protein, 36 grams carbohydrates, 52 grams fat, 797 milligrams sodium, 173 milligrams cholesterol.