Heat oven to 375 degrees F. Butter a 1 1/2 to 2-quart baking dish and sprinkle with just a bit of the shallot.
Add the heavy cream to a medium saucepan along with the remaining shallot, garlic, salt and pepper. Place over medium heat and bring to a simmer while stirring. Let simmer until you see the liquid begin to thicken, 2 to 3 minutes.
Layer 1/3 of the sliced potatoes in the baking dish, cover with some Cheddar and a sprinkling of Parmesan; repeat the layering 2 more times.
Pour the hot liquid over the potatoes. Add the remaining cheese, cover with foil, and bake for 1 hour, then remove the foil to bake until the cheese is golden and brown, 15 to 20 minutes. Let rest for 10 minutes before slicing so it can settle.
Recipe courtesy of The Neelys