Preheat the oven to 450 degrees.
In a blender combine milk, flour, cheese, 3 eggs, cornstarch, ½ teaspoon salt, and pepper. Turn the blender on medium speed and blend until combined. If using a glass bowl then whisk by hand.
Place a 10-inch cast iron skillet over high heat until almost smoking, about 1 minute. Add 2 tbsp. butter and let melt, about 5 seconds. Tilt to coat the entire surface of the pan with the melted butter. Immediately pour the batter into the center of the pan and cook for 3-4 min. or when edges begin to form.
Carefully transfer the pan to the oven. Cook until the pancake is puffed and golden brown in the center, about 7-10 minutes.
Meanwhile, place a non-stick pan over medium heat with 1 tbsp. olive oil. Crack the 2 remaining eggs into the pan and cook to desired doneness. Set aside.
Serve the pancake in the same pan and top with the prosciutto, avocado, fried eggs, shallots and Parmesan cheese. Season to taste with Kosher salt and black pepper. Serve immediately.
(Optional) Serve in Le Creuset oval pan