Preheat the oven to 375 degrees F. Grease an 11 inch tart shell with butter or oil.
In a saucepan, bring the yellow grits and water to a boil, then cook for 2 minutes, stirring frequently. Season to taste with salt and pepper. Spread the grits evenly out into the pan, using a flat turner or knife to straighten up the edge.
Bake for 20 minutes. Take the tart out of the oven and let it cool slightly, and increase oven temperature to 400 degrees F.
Whisk to combine the eggs, bacon, scallions, mascarpone, and cheddar cheese. Add a generous pinch of salt and pepper, and pour the mixture into the grits tart shell.
Bake for 15 minutes until slightly browned on top. Serve and enjoy!