Preheat the Oven – Set the oven rack to the center position. Preheat to 350ºF (177ºC). Grease a 9×13-inch baking dish with oil or cooking spray on the bottom and sides.
Mix the Ingredients – To the baking dish, evenly spread the frozen tater tots, ham, 1 cup cheddar cheese, and green onions.
Add the Egg Base – In a large bowl, whisk together the cornstarch, 1 teaspoon salt, garlic powder, onion powder, paprika (if using), and black pepper. Add the eggs and whisk to combine. Whisk in the half-and-half. Pour the egg mixture into the baking dish. Evenly sprinkle the remaining 1 cup of cheese on top.
Bake the Casserole – Bake for 45 to 55 minutes, until the center sets and a toothpick inserted comes out clean. The internal temperature should be 180 to 190ºF (82 to 88ºC). Cool for 10 minutes before slicing and serving.
Notes
Omitting Cornstarch: The custard will be less tender. Make sure to bake at the recommended temperature to prevent a rubbery texture.
Make Ahead: Assemble the casserole, then tightly press a piece of plastic wrap against the potato mixture. Refrigerate for up to 1 day.
Storing: Cover and refrigerate leftovers in an airtight container for up to 3 days.
Reheating: Reheat in the microwave on high setting in 15 to 30-second increments until hot.