Feta-Stuffed Burgers with Grilled Onion on Sourdough

Ingredients

• 0.3 teaspoon pepper black divided
• 4 slices crusty sourdough bread 
• 4 teaspoons dijon mustard coarse-grained
• 2 tablespoons olive oil extra virgin divided
• 2 ounces feta cheese cut into 4 (1/2-ounce) pieces
• 1.5 pounds ground beef lean
• 12 slices plum tomatoes 
• 4 slices onion red (1/4-inch-thick)
• 0.8 teaspoon salt divided

Equipment

• frying pan
• grill pan

Directions

1. Sprinkle beef with 3/4 teaspoon salt and 1/4 teaspoon pepper; gently mix, and shape into 8 thin patties.
2. Place 1 piece feta cheese in center of each of 4 patties. Top with remaining 4 patties, pressing edges to seal.
3. Brush onion slices with 2 teaspoons oil, and sprinkle with the remaining 1/8 teaspoon salt and 1/8 teaspoon pepper. Cook on a lightly greased grill pan or in a skillet over medium-high heat 4 minutes on each side or until tender and slightly charred.
4. Transfer to a plate, and keep warm.
5. Add burgers to pan; cook 6 minutes on each side.
6. Transfer to a plate, and keep warm.
7. Brush bread slices with remaining 4 teaspoons oil.
8. Add to pan, and toast about 1 minute on each side or until lightly golden.
9. Spread Dijon mustard evenly on 1 side of each bread slice. Top each with 1 onion slice, 3 tomato slices, and 1 burger.
10. Serve immediately.