1 sheet of puff pastry
2 cups sliced mushrooms
1 leek, thinly sliced
1 tbsp olive oil
1/2 cup grated Gruyère cheese
2 eggs
1/2 cup heavy cream
Salt and pepper to taste
Fresh thyme for garnish

1. Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper.
2. Roll out the puff pastry and place it on the prepared baking sheet.
3. In a skillet, heat olive oil over medium heat and sauté the mushrooms and leeks until softened. Season with salt and pepper.
4. Spread the mushroom and leek mixture over the puff pastry, leaving a border around the edges.
5. In a bowl, whisk together eggs, heavy cream, and half of the Gruyère cheese. Season with salt and pepper.
6. Pour the egg mixture over the mushrooms and leeks, and sprinkle the remaining cheese on top.
7. Bake for 25-30 minutes or until the tart is golden and set.
8. Garnish with fresh thyme before serving.