1. Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.

2. In a large bowl whisk flour, sugar, baking powder, baking soda, and salt.

3. Cut cold butter into the dry mixture until it resembles coarse crumbs.

4. In a separate bowl combine sourdough discard, buttermilk, vanilla extract, and lemon zest.

5. Pour wet ingredients into dry and stir gently until just combined.

6. Turn dough onto a floured surface and pat into a 1-inch thick rectangle.

7. Cut with a biscuit cutter into rounds and place on the prepared sheet.

8. Brush tops with buttermilk and sprinkle with sugar.

9. Bake 15–18 minutes until golden and cool on a rack.

10. Meanwhile, combine rhubarb, strawberries, sugar, and lemon juice in a saucepan.

11. Simmer over medium heat for 8–10 minutes until thickened, then stir in optional vanilla.

12. Whip cream with powdered sugar and vanilla until soft peaks form.

13. Split cooled shortcakes, layer with compote and whipped cream, then top and serve immediately.