In a large saucepan over medium-high heat, combine the milk, garlic powder, salt, white pepper and Tabasco. Heat, stirring slowly and constantly, until the milk just comes to a boil. Add the grits and stir to mix. Reduce the heat to low, cover and cook until the mixture is thick and creamy, 5 to 6 minutes.
Add the cheeses and stir until they melt completely. Serve warm.