French Onion Baked Potatoes

0 Boil the Potatoes: Fill a large pot with water and bring to a boil. Add the potatoes and cook until mostly tender, about 30 minutes. Transfer immediately to an ice bath to cool completely, then drain and pat dry with paper towels.
1 Make the Onion Filling: Heat the butter and avocado oil in a large skillet over medium heat. Add the sliced onions and cook, stirring often, for about 12 minutes until softened and lightly caramelized. Add the seasoned salt and brown sugar and continue cooking for about 5 minutes until deeper in color. Add the thyme sprig, bay leaves, white wine, and beef broth. Cook until the liquid reduces and the onions are well coated and jammy. Remove and discard the thyme sprig and bay leaves.
2 Prepare and Bake: Preheat the oven to 450°F. Dry and then cut the cooled potatoes in half lengthwise. Use a spoon to gently scoop out a small well in the center of each half. Arrange the potato halves cut side up on a baking sheet and brush lightly with olive oil. Bake for about 15 minutes, until the edges are lightly crisped.
3 Assemble and Finish: Top each potato with a few very thin slices of Gruyere, a spoonful of the onion filling, then add another layer of Gruyere. Finish with Parmigiano Reggiano and a pinch of fresh thyme leaves. Return to the oven and broil just until the cheese is melted and golden. Remove from the oven, finish with chopped chives and some fresh cracked pepper.