1. Combine flour and salt in a bowl, cut in cold butter until mixture resembles coarse crumbs

2. Stir in sourdough starter discard, then add ice-cold water a tablespoon at a time until dough just holds together

3. Gather dough into a disk, wrap in plastic, and chill for at least 45 minutes

4. Lightly flour surface, roll chilled dough into a roughly 12-inch circle and transfer to a parchment-lined baking sheet

5. In a skillet, sauté apple slices with butter, sugar, cinnamon, nutmeg and lemon juice until slightly softened, then cool

6. Arrange apple filling in the center of dough, leaving a 2-inch border, fold edges over the fruit

7. Brush crust with egg wash, sprinkle raw sugar over crust and apples

8. Bake at 400°F for 35 to 45 minutes until crust is golden and juices bubble

9. Transfer galette to a wire rack, cool for 15 minutes and serve warm with ice cream or whipped cream