1. Preheat oven to 350°F (175°C) and line a 9×9-inch pan with parchment paper.

2. In a large bowl whisk together flour, brown sugar, salt, cinnamon, and nutmeg.

3. Add cold butter and use a pastry cutter or fingers to work into mixture until coarse crumbs form.

4. Stir in sourdough discard and vanilla until dough holds together when pressed.

5. Press two-thirds of the dough firmly into the bottom of the prepared pan.

6. In a saucepan combine apples, remaining brown sugar, cinnamon, butter, and lemon juice.

7. Cook over medium heat, stirring, until apples soften and juices thicken, about 5–6 minutes.

8. Spread apple filling evenly over the crust layer.

9. In a bowl mix reserved dough with oats, pecans, and a pinch of cinnamon to form the crumble topping.

10. Sprinkle the crumble mixture evenly over the apple layer without pressing down.

11. Bake for 35–40 minutes until topping is golden brown and filling bubbles.

12. Cool in pan on a rack for at least 20 minutes before lifting out and slicing into bars.

13. Serve warm or at room temperature, optionally with whipped cream or vanilla ice cream.