01 - Combine flour and salt in a mixing bowl. Add cold, cubed butter and rub it in with fingertips until the mixture resembles coarse crumbs. Gradually add cold water, one tablespoon at a time, until the dough just comes together. Shape into a disk, wrap, and refrigerate for 20 minutes.
02 - Heat oven to 375°F (190°C).
03 - Roll chilled pastry dough to 1/8 inch thickness. Cut out circles sized to fit six 4-inch tartlet pans. Press dough firmly into pans, trim the excess, and prick bases with a fork. Line with parchment and fill with baking weights or dried beans. Bake for 10 minutes, then remove weights and parchment and bake for another 5 minutes.
04 - Heat olive oil in a skillet over medium heat. Sauté diced shallot until soft, about 2 minutes. Add sauerkraut and cook for an additional 2 minutes. Remove from heat.
05 - In a bowl, whisk together pumpkin purée, white miso paste, heavy cream, eggs, ground black pepper, and nutmeg until smooth and homogenous.
06 - Evenly distribute the sauerkraut mixture among the pastry shells. Spoon the pumpkin-miso custard over the sauerkraut, and sprinkle each tartlet with grated Gruyère or Emmental cheese.
07 - Bake tartlets for 20 to 25 minutes, or until the filling is set and the tops appear lightly golden. Allow to cool slightly before removing from pans.
08 - Top tartlets with finely chopped fresh chives if desired. Serve warm or at room temperature.