This beautifully simple pastry is very apple-forward. Where you might expect to taste cinnamon along with the apple, you'll discover the flavors of butterscotch and toasted pecans. Semolina and buttermilk in the pastry make it golden, tender, and very easy to roll out.
Preheat the oven to 400°F. Line a baking sheet with parchment.
To make the crust: In a medium bowl, combine the flour and semolina with the sugar and salt. Work in the cold butter until it’s in pea-sized chunks. Gradually stir in the buttermilk, using a fork. Start with 4 tablespoons, adding more as needed to bring the dough together. Gather the dough into a disk, pat it 3/4" thick, wrap, and chill for at least 1 hour.
Roll the chilled pastry into a 13" round, 1/4" thick. Place the round on the prepared baking sheet.
To fill and assemble: Sprinkle the flour and salt over the pastry, leaving a 1" border uncovered at the edge. Spread the pecans in a 9" circle in the center of the dough.
Arrange the apples in concentric circles over the nuts. Sprinkle the apples with sugar. Bring the pastry up and over the apples to make a top crust, leaving the center uncovered. Dot the apples in the center with butter.
Brush the top crust with the beaten egg mixture and sprinkle generously with coarse sugar.
Bake the galette for 25 minutes, until it's golden brown. Remove it from the oven and let it cool to lukewarm before serving.
Store refrigerated for up to five days; freeze for up to three months.
Don't have fresh buttermilk for the crust? Substitute 1 tablespoon buttermilk powder (added along with the flours) and 4 to 6 tablespoons ice water for the cold buttermilk called for in the recipe.
