Mini Frittatas with Leeks and Asparagus

Name: Mini Frittatas with Leeks and Asparagus
Cuisine: European, Italian, Mediterranean
Ingredients: Cooking spray; 1 tablespoon olive oil; 1 medium leek, white part only, chopped (2 cups); 1 bunch asparagus (1 pound), sliced on the bias into ½-inch pieces (2 cups); 6 medium white button mushrooms, sliced (4 ounces); 7 large eggs; ¼ cup 1% low-fat milk; ¼ cup grated Parmesan cheese; ½ teaspoon salt; 1/8 teaspoon freshly ground black pepper