2 tablespoons unsalted butter, plus more for the baking dish
2 3/4 pounds baking potatoes, such as russets, peeled, sliced into 1/8-inch-thick slices
8 pork loin chops (about 9 to 10 ounces and 1 inch thick)
Kosher salt and freshly ground black pepper
Heat a large pot over medium heat. Add the butter and stir until melted. Add the onions, garlic, and thyme and sauté for about 5 minutes, or until the onions are tender but have not taken on any color. Add the cauliflower and cook for about 6 minutes, stirring often, or until softened. Add the cream and milk and bring to a simmer. Add the cheese and stir until it melts, then remove from the heat and discard the thyme stems.
Working in batches, puree the mixture in a blender; return to the pot. Season generously to taste with salt and pepper.
Stir the potato slices into the hot cream mixture to coat. Spoon 1 cup of the cream mixture into the baking dish. Spread the potatoes and the remaining cream mixture evenly in the dish. Cover with aluminum foil and put on a rimmed baking sheet. Bake for about 1 hour, or until a knife can be inserted easily into the potatoes. Uncover the dish, raise the oven temperature to 400°F, and continue baking for about 10 minutes, or until golden brown on top. Remove from the oven and let stand for 10 to 20 minutes.
Season the pork chops with salt and pepper. Grill for about 5 minutes per side, or until the pork shows only the barest hint of pink when pierced at the bone with the tip of a sharp knife. Transfer to a platter and let stand for 5 minutes before serving with the gratin.