Preheat oven to 375 degrees. In a medium sized bowl beat eggs, milk, 1 teaspoon salt, and 1/8 teaspoon pepper, and set aside. Grease two muffin tins with butter or oil. In a large skillet, heat olive oil on medium heat. Cook onions 2-3 minutes until slightly soft. Add sweet potatoes and cook about 4-6 minutes until soft. Add Swiss chard and rosemary, and cook another 4 minutes or so, until greens are all wilted. Add additional salt and pepper to taste. Fill the bottom of each muffin tin with about a tablespoon of cooked vegetables. Spread the vegetables evenly until all 24 cups are filled. Place 1-2 tablespoons of egg mixture into each of the cups, nearly covering the vegetables. Bake about 10-12 minutes. Take tins out and sprinkle a pinch of parmesan cheese on each little frittata. Place back in the oven for another approximately 5 minutes until cooked through (watch carefully so they don’t brown too much). Remove each frittata with a silicone spatula and serve warm.