Spring Potato Strata

Name: Spring Potato Strata
Ingredients: nonstick cooking spray; 2 tablespoons butter or 2 tablespoons margarine; 3 medium leeks, thinly sliced; 5 cloves garlic, finely chopped; 2 cups coarsely chopped red bell peppers; 1 (8 ounce) packagesliced mushrooms; 2 1⁄2 lbs potatoes, cut into 1/4-inch thick slices; 2 1⁄2 cups shredded fontina or 2 1⁄2 cups shredded swiss cheese, , divided; 5 large eggs, lightly beaten; 1 1⁄4 cups milk; 1 1⁄2 teaspoons salt; 1⁄2 teaspoon pepper; 1⁄2 teaspoon dried thyme leaves, crushed (optional)