Crust - Place the flour, salt and cold butter that has been shaved with a cheese grater into a small bowl. Use a pastry cutter, or 2 knives, to cut the butter into the flour until it resembles small crumbs. Add the ice water 1 tablespoon at a time until the dough comes together and forms a ball. Set aside.
Preheat the oven to 400 degrees. Roll out the pastry dough and fit into the base of a 9” tart pan with a removable bottom. It’s helpful to place the tart pan on a baking sheet in case any of the filling bubbles out.
Scrub the outside of the potatoes well, or if desired, they can be peeled, I prefer with the skin. CAREFULLY slice using a mandolin into very thin pieces, about ⅛” thick. (A knife will work as well, just try to make the slices even so they cook at the same pace.)
Mix the cream, nutmeg, garlic and salt in a small bowl. Spread the sour cream over the pie crust in the pan and arrange the potatoes in an artful way with the slices slightly overlapping each other, covering the entire inside of the tart pan. (kinda' like they look like a flower)
Pour the cream mixture over the top and if desired, sprinkle salt and pepper to taste. Dot the tops with small pats of butter and place in the oven to bake for 40 minutes, or until golden brown and bubbly. (if you wanted to make cheesy sprinkle about 3/4 c. shredded cheese on top 10 minutes before it's done to melt and brown)
Allow to cool slightly before slicing and serving.