1/2 cup dijon mustard 1 Tablespoon fresh grated horseradish 1 large sweet onion Olive oil Salt and fresh ground pepper About 1-1/4 pounds hamburger Four 1/4" thick slices of sharp cheddar cheese 1 beefsteak tomato, cut into 1/4" slices 4 lettuce leaves, washed and dried
Prepare a grill. In a small bowl, mix together dijon mustard and horseradish.
Brush onion slices on both sides with oil and season with salt and pepper. Place on grill over hot coals or high heat and grill until golden, about 4 minutes on each side.
Divide hamburger into 4 patties and season on both sides with salt and pepper. Place on grill and cook for 4-5 minutes per side. During the last few minutes of grilling, top each pattie with a slice of cheese. Cover grill and let cheese melt.
To serve, cover each plate with a lettuce leaf, then a hamburger pattie w/ melted cheese, then tomato and finally the onion slice. Place a dollop of horseradish mustard on top of the onion and serve immediately.
You can use prepared horseradish, just make sure it is gluten-free.