Preheat the oven to 450 degrees F.
Place the potatoes in a medium pot, cover with water by one inch, add 1 tablespoon salt, and bring to a boil. Simmer for 10 to 15 minutes, until the potatoes are barely tender when tested with a wooden skewer. Drain and cover with a kitchen towel to steam for 5 minutes. Cut in half lengthwise and set aside.
Meanwhile, heat 2 tablespoons olive oil over medium heat in a large sauté pan, add the prosciutto, and cook for 5 minutes until beginning to crisp, turning occasionally. Remove prosciutto to a plate covered in paper towel. Add the onions to the pan, and toss to combine with the fat. Saute' over medium heat until softened. Off the heat, add the potatoes, stir in the wine, 1 1/2 teaspoons salt, and 1/2 teaspoon pepper.
Divide the potatoes and onion mixture, then the crispy prosciutto among four gratin dishes. Top with apple slices. Arrange the raclette in one layer over the potatoes, prosciutto and apples. Distribute the thyme sprigs on top. Bake for 10 to 12 minutes, until the cheese is hot and bubbly.
Remove the gratins from the oven, and serve hot with crusty bread.