3lbyellow potatoes, thinly sliced (peeled or unpeeled)
Preheat oven to 350°F. Lightly grease 9x13 casserole dish.
In a medium pot, melt the butter over medium heat. Add the onions and garlic; cook 5 minutes. Whisk in the flour; cook an additional 1 minute while whisking.
In a small bowl, combine the cream, milk and broth. Slowly pour the cream mixture into the pan in a thin steady stream while whisking. Stir in the salt and pepper. Bring to a low boil. Reduce heat and simmer, stirring occasionally until slightly thickened, about 5 minutes.
Layer half of potatoes into prepared dish, season with additional salt and pepper. Pour half the cream mixture over top. Press the potatoes down with the back of a wooden spoon and repeat layers with the remaining half of potatoes and cream. Press potatoes down again.
Bake covered 30 minutes, uncover and bake an additional 45 minutes, until potatoes are tender. Remove from oven and sprinkle top with Parmesan. Bake 5 more minutes. Remove from oven and let potatoes rest 10 minutes before serving.