1. Combine the flours and 3/4 teaspoon salt in a food processor and pulse once or twice. Add 6 tablespoons of the oil and turn on the machine; process until the oil and flour are blended and the mixture looks like cornmeal, about 10 seconds. With the machine running, slowly add the ice water, stopping as soon as the mixture stays together when pinched (you may not need all of it).
2. Turn the dough out onto a lightly floured work surface and form into a ball. Wrap in plastic and refrigerate for at least 30 minutes. (You can refrigerate the dough for up to a couple of days or freeze, tightly wrapped, for a couple of weeks.)
3. Make shallow cuts on the flat side of each chestnut and put them in a large pot with enough water to cover. Add a pinch of salt and bring to a boil. Cook, stirring once or twice, until the shells soften, about 10 minutes, then turn off the heat. When they’re cool enough to handle, remove a few chestnuts and peel off the outer and inner skins. Transfer the meat to a food processor, sprinkle with salt and pepper, and puree, adding water 1 tablespoon at a time, until it is the consistency of cream cheese; taste and adjust the seasoning. Transfer to a bowl and refrigerate. Rinse out the food processor and use the slicing blade to shred the Brussels sprouts.
4. Put 3 tablespoons oil in a large skillet over medium heat. When it’s hot, add the shallots and cook until golden and soft, 15 to 20 minutes. Add the sprouts, the apple, and wine and sprinkle with salt and pepper; cook, stirring occasionally, until the wine has cooked off and the mixture is quite soft, 15 to 25 minutes. Stir in the chestnut puree and the sage, taste, and adjust the seasoning.
5. Heat the oven to 350°F. Line a large baking sheet with parchment paper. Sprinkle a clean countertop with flour, unwrap the dough, and sprinkle the top with flour. If the dough is hard, let it rest for a few minutes. Use a rolling pin to roll with light pressure from the center out to 1/4-inch thickness, rotating the dough slightly after each roll and adding flour only if the dough is sticking. Loosely roll the dough onto the rolling pin and transfer to the prepared baking sheet.
6. Spread the vegetable mixture on the dough, leaving a 3-inch border all around. Lightly smooth the filling so it is the same thickness all over. Fold the sides up around the filling (you should have a big open circle at the top). Refrigerate the galette for 30 minutes.
7. Brush the top of the dough with the remaining tablespoon oil. Bake the galette until the crust is browned and the filling is steaming hot, 40 to 50 minutes. Cool a bit before slicing and serve hot or at room temperature.

— Recipe from Dinner for Everyone: 100 Iconic Dishes, Made 3 Ways — Easy, Vegan, or Perfect for Company