Heat oven to 375 degrees F.
In a large bowl, stir together corn, eggs, cheeses. In a second bowl, whisk together half and half, cornstarch, garlic, salt, and pepper. Add this mixture to the corn mixture. Stir well.
Pour into an 8x13” baking dish. Bake for 40-50 minutes, or until the edges turn golden brown and the center of the casserole is set.
Top with sour cream and sour cream. Garnish with a sprinkling of chili powder, if desired.