Prepare the Cream Mixture

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Heat the Cream: In a small saucepan, combine the heavy cream, milk, minced garlic, butter, salt, pepper, and nutmeg. Heat over medium-low heat, stirring occasionally, until the butter melts and the mixture is warm. Set aside.

Assemble the Mini Gratin

1. Grease the Ramekins: Lightly grease 4 small ramekins (or a muffin tin) with butter.
2. Layer the Potatoes: Arrange the sliced potatoes in overlapping layers in each ramekin, slightly pressing them down as you go. Continue layering until the ramekin is full.
3. Add the Cream: Pour the warm cream mixture over the potatoes, making sure the slices are well-coated.
4. Add the Cheese: Sprinkle the shredded Gruyère cheese generously on top of each ramekin.

Bake the Gratin

1. Bake in the Oven: Place the ramekins on a baking sheet and bake for 40-45 minutes, or until the potatoes are tender and the top is golden and bubbly. You can check the doneness by inserting a knife into the potatoes; it should slide in easily when done.

Serve

1. Garnish and Serve: Let the gratins cool for a few minutes before serving. Garnish with fresh thyme sprigs, if desired, and serve hot.