Put milk, cream, 2 3/4 c. shredded cheddar cheese, water, butter, and salt in a large pot and stir. Bring to a boil over medium heat, stirring often.
Remove from heat and whisk in instant potato flakes.
Whisk eggs with garlic powder, sour creamStir in beaten eggs.
Spread into a greased 9″x 9″ baking dish and bake at 350˚F for 30-35 minutes, until puffy and golden.