Mix flour, parmesan, and salt in a large bowl until well combined. Cut in butter until coarse, large crumbs form. Add cold water and mix gently until evenly moistened. If needed, add more water 1 tablespoon at a time. Shape into a disk, then wrap in cling wrap. Refrigerate for at least 1 hour.
Heat oven to 425°F.
Clean sweet potatoes and bake for 30 to 35 minutes, or until soft but firm in the middle. Check the center by piercing it with a knife. Set aside until cool enough to handle, then peel and cut into ⅛-inch slices.
Onto a lightly floured work surface, roll out dough into a 12-inch circle about ¼-inch thick. Transfer to a parchment-lined baking sheet and brush with 1 tablespoon of olive oil.
Meanwhile, rub the kale with 1 teaspoon of olive oil.
Leaving a 2-inch space from the edge, spread the mustard in a thin layer in the center of the dough, then add half of the raclette. Layer and overlap sweet potatoes in the center, followed by remaining raclette, kale, and sausage. Season with salt and pepper and sprinkle with thyme. Fold the edges toward the center to frame the filling. Brush the edges with the egg mixture.
Bake for 25 to 35 minutes, or until golden brown and bubbling.
Remove from oven and cool for 10 minutes. Slice and top with red cabbage slaw and cornichons.
