Peel and cube the potatoes into about 1 inch cubes. In a mixing bowl, add the cream, flour, garlic, salt, and pepper together with 1/4 cup cheddar cheese and 1/4 cup of the Gruyere. Add the potatoes and coat evenly. Grease serving size ramekins or oven safe dish with butter. Divide the potato mixture evenly among the dishes, making sure that the cream is also evenly distributed. Top with the remaining Gruyere and Cheddar cheese, and a sprinkle of more pepper. Cover with foil and bake at 400 degrees F for about 35 minutes. Remove the foil and allow the gratin to brown and crisp for another 15 to 20 minutes!