Ingredients:
- All-purpose flour, for dusting
- Two 6-ounce balls of levain dough (sourdough; see Note)
- Extra-virgin olive oil, for brushing and drizzling
- 1/4 cup crème fraîche
- 1/4 pound Red Norland or other red potatoes, sliced crosswise 1/16 inch thick on a mandoline
- 1/4 cup lightly packed rosemary leaves
- 2 teaspoons finely grated lemon zest, preferably Meyer lemon
- Maldon sea salt (see Note)
- Freshly ground black pepper