Creating a Rustic Honeycrisp Apple Galette is a straightforward process, and following these steps will ensure your success:

1. Preheat Oven: Begin by preheating your oven to 375°F (190°C).
2. Prepare Apples: In a large bowl, combine the sliced Honeycrisp apples with lemon juice, granulated sugar, cinnamon, nutmeg, flour, and vanilla extract. Toss until the apples are well coated.
3. Roll Out Dough: If using homemade pie crust, roll it out on a lightly floured surface into a rough circle about 12 inches in diameter. If using store-bought, simply unroll it.
4. Arrange Apples: Transfer the rolled dough to a parchment-lined baking sheet. Spoon the apple mixture onto the center of the dough, leaving a 2-inch border around the edges.
5. Fold Edges: Gently fold the edges of the dough over the apples, creating a rustic border. Make sure to leave the center open.
6. Egg Wash: Whisk the egg in a small bowl and brush it over the folded edges of the crust for a golden finish.
7. Sprinkle Sugar: If desired, sprinkle coarse sugar over the crust for added crunch and sweetness.
8. Bake: Place the galette in the oven and bake for 40-45 minutes, or until the crust is golden brown and the apples are tender.
9. Cool: Once baked, remove the galette from the oven and allow it to cool for 15-20 minutes on the baking sheet.
10. Slice and Serve: After cooling, slice the galette and serve warm or at room temperature.