Directions

1. Stir the flour and salt together in a KitchenAid® stand mixer to combine. Add the olive oil and mix on low speed with the whip attachment, until the mixture resembles coarse meal. Toss in the butter slices and shake to coat. Switch to the dough hook attachment. Mixing on low speed, dribble in the ice water a tablespoon at a time, until the mixture is just beginning to hold its shape. Form the dough into a ball and roll it into an oblong shape on a lightly floured work surface. Fold into thirds, roll again, and fold into thirds once again. Refrigerate for at least 30 minutes, and up to several days.
2. Cream the butter and sugar on medium-high speed, using the paddle attachment, until pale and fluffy. Add the walnuts and flour and mix until incorporated. Mix in the egg, liqueur, and salt until smooth.
3. Slice the fruits to a thickness of ¼ inch, discarding the tops and bottoms. Layer evenly in a medium saucepan. Pour the juice over and place on medium heat until it begins to boil. Turn the heat to low and simmer for 20 minutes, swirling the pot occasionally. Sprinkle the sugar over the surface, and simmer for another 20 minutes, swirling occasionally, until the fruit is soft and the juice is syrupy.
4. Preheat the oven to 350 degrees F. Roll the pie dough to a thickness of 1/8 inch. Transfer to a pie plate. Spread the walnut filling evenly in the center of the dough, leaving a 3 inch margin all around the edge. Top with citrus. Fold up the sides, pleating as needed. Brush the dough with egg wash (1 egg beaten with 2 teaspoons water), and sprinkle with sparkling sugar. Chill the galette (if necessary), and bake for 45 minutes.