Peel potatoes and slice thinly. I used a mandoline with 1.5 mm blade.
In a 4-cup measuring cup add whipping cream, egg, garlic powder, nutmeg and thyme (if using). Stir until combined. Set aside.
Brush an 8-inch square, glass baking pan (or 2 loaf pans) with oil. Line pan with parchment paper leaving enough excess over 2 sides to cover the pan while cooking.
Starting with orange potatoes layer them slightly overlapping to cover the bottom of the pan.
Top each layer with salt and pepper, a generous sprinkling of cheese and some of the cream mixture.
Repeat alternating orange and white potatoes until you have 6 layers, 3 orange and 3 white.
Sprinkle top layer with remaining cheese and cream mixture.
Fold parchment over the potatoes and cover with foil. Can be prepared in advance to this point.
Bake in preheated oven for 90 minutes.
Let rest in the pan for 15-20 minutes. Using parchment transfer cooked potatoes to cutting board. Cut and serve hot. Garnish with fresh thyme if desired.
Notes
Readers say these scalloped potatoes can be cooked in advance, then frozen and reheated. Perfect for large gatherings.