Preheat the oven to 200°C (400°F).

Roll out the puff pastry on a lightly floured surface to fit a tart pan. Place the pastry into the tart pan and trim the edges. Prick the base with a fork and set aside.

In a large skillet, heat the olive oil over medium heat. Add the sliced leeks and sauté for about 5-7 minutes until they are softened and translucent. Season with salt and pepper. Remove from heat and let cool slightly.

In a mixing bowl, whisk together the eggs and heavy cream. Season with a little more salt and pepper.

Spread the sautéed leeks evenly over the puff pastry base. Pour the egg and cream mixture over the leeks, ensuring they are evenly coated.

Scatter the pieces of Camembert cheese on top of the mixture.

Bake in the preheated oven for 30-35 minutes, or until the tart is golden brown and set in the center.

Remove from the oven and let cool for a few minutes. Garnish with fresh thyme leaves if desired.

Slice and serve warm, or at room temperature.