01 -  Preheat the oven to 375°F (190°C) to ensure even cooking. 
 02 -  In a large mixing bowl, whisk together the eggs and milk until well combined. 
 03 -  Fold in the diced ham, chopped spinach, and shredded cheddar cheese. Season lightly with salt and freshly ground black pepper if desired. 
 04 -  Pour the mixture into a lightly greased 9-inch ovenproof nonstick skillet or baking dish, spreading ingredients evenly. 
 05 -  Place in the oven and bake for 20 to 25 minutes, or until the frittata is set in the center and lightly golden on top. 
 06 -  Allow to cool briefly before slicing into wedges and serving warm.