Instructions:
- Prepare the Dough: Whisk the flour, salt, and optional yeast in a bowl. Add the warm water and oil; mix until a shaggy dough forms. Knead briefly (about 3 minutes) until smooth.
- Cover the dough and let it rest at room temperature for 30 minutes, or chill for up to 24 hours for better flavour.
- Preheat & Prep Baking Surface: Place your pizza stone or steel in the oven. Preheat oven to the highest possible temperature (500–550°F / 260–290°C) for at least 45 minutes.
- Prepare Toppings: Stir the crème fraîche with salt, pepper, and thyme (if using). Quickly sauté the lardons/pancetta for 2 minutes just to release a bit of fat.
- Stretch the Dough: Divide the dough in half. On a lightly floured surface, roll or stretch one half into a very thin, roughly rectangular or oval shape (about 1/8 inch thick).
- Assemble the Tart: Dust your pizza peel heavily with semolina or flour. Carefully transfer the stretched dough onto the peel. Spread half of the crème fraîche mixture evenly, leaving a small border.
- Top the assembled dough with half of the thinly sliced onions and half of the sautéed lardons.
- Bake Rapidly: Quickly slide the Flammkuchen from the peel onto the preheated stone. Bake for 8–12 minutes until the crust is beautifully puffed, blistered, and golden brown.
- Remove from the oven. Repeat steps 5–8 with the remaining dough and toppings. Serve piping hot immediately.