Crusted Portabella Burgers

Ingredients

• 2 large egg whites
• 1 tablespoon olive oil
• 1/3 cup Italian-style fine dried bread crumbs
• 2 tablespoons chili powder
• 4 portabella mushroom caps (5 in. wide; 1 to 1 1/4 lb. total)
• 4 round sandwich buns (4 in. wide; 3/4 lb. total)
• 1 cup nonfat sour cream
• 2 teaspoons minced canned chipotle chilies or hot sauce
• 1/4 cup thinly sliced red onion
• 1 cup spinach leaves, rinsed and crisped
• Salt
• Pepper

Preparation

1. 1. In a bowl, beat egg whites and oil to blend. In another bowl, mix crumbs and chili powder.
2. 2. Rinse mushroom caps; drain. Coat each cap with egg mixture, drain briefly, then coat with crumbs, shaking off excess. Set caps, gill sides down, slightly apart on a 12- by 15-inch baking sheet. Lay bun halves, cut sides up, side by side on another 12- by 15-inch baking sheet.
3. 3. Bake mushroom caps in a 450° oven until browned and flexible when pressed, about 20 minutes. About 3 minutes before mushrooms are done, add buns to oven; bake until lightly toasted.
4. 4. In a small bowl, mix sour cream and chipotle chilies. Spread mixture on cut sides of buns. Layer equal amounts of onion and spinach on each bun bottom, top with a mushroom cap, add salt and pepper to taste, and cover with bun top.