Cook bacon in a skillet over medium heat until crisp. Remove bacon; drain and crumble. Transfer 2 teaspoons bacon drippings to a saucepan.
Bring drippings, milk, and butter to a boil over medium heat. Gradually whisk in grits, 1 teaspoons kosher salt, and 1/2 teaspoons pepper; cook, whisking constantly, 15 minutes or until very thick. Remove from heat; let stand 10 minutes. Stir in 1 cup cheese; let stand 10 minutes. Stir in 1 egg; spread in a 9" springform pan coated with cooking spray.
Bake for 25 minutes or until set and browned. Sprinkle remaining 1 1/2 cups cheese over warm grits, spreading to edges. Let stand for 15 minutes.
Reduce oven temperature to 325 degrees.
Combine half-and-half, cream, green onions, and remaining 5 eggs, 1 teaspoons kosher salt, and 1/2 teaspoons black pepper. Pour over grits; sprinkle with crumbled bacon. Place pan on a foil-lined baking sheet.
Bake for 1 hour and 15 minutes or until lightly browned and just set. Let stand 20 minutes. Run a sharp knife around edges of quiche; remove sides of pan.