1. Combine flour, salt, and cold butter and rub until mixture is crumbly.

2. Add sourdough starter and cold water, mixing gently until dough forms.

3. Shape dough into a disc, wrap, and refrigerate for 30 minutes.

4. Preheat oven to 375°F (190°C).

5. Roll dough to 1/8-inch thickness and cut circles slightly larger than tart pans.

6. Press dough circles into tart pans and prick bases with a fork.

7. Fill each cup with a piece of brie and a spoonful of cranberry sauce, then sprinkle with thyme.

8. Chill assembled tartlets for 10 minutes.

9. Bake for 20–25 minutes until crust is golden and filling bubbles.

10. Cool on a wire rack and garnish with rosemary sprigs, black pepper, and sea salt flakes.