How to Make It
Toss sliced potatoes with flour in a large bowl until potatoes are coated.
Saute garlic and shallot with crushed red pepper in butter in a Dutch oven 2 minutes. Add coated potatoes, milk, and next 3 ingredients, stirring well. Bring to boil; reduce heat and simmer until thickened.
Spoon half of potato mixture into lightly greased 3-quart au gratin dish. Sprinkle mixture with half of Gruyere cheese. Repeat procedure with remaining potatoes and Gruyere cheese. Top with Parmesan cheese. Cover and bake at 350F for 30 minutes. Uncover and bake 35-40 minutes more until potatoes are tender and cheese is browned.