1. Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.

2. Trim the woody ends of the asparagus, rinse, pat dry, and place in a single layer on the prepared sheet.

3. Drizzle the asparagus with olive oil, sprinkle with salt, pepper, lemon zest, minced garlic, and thyme, then roast for 10–12 minutes until tender and lightly charred.

4. While the asparagus roasts, melt the butter in a small saucepan over low heat, whisk in lemon juice and zest, then remove from heat to keep the sauce silky.

5. Lightly toast the sourdough slices or par-bake the crust for 5 minutes, then brush with olive oil or a thin layer of lemon butter.

6. Arrange the roasted asparagus in neat rows on the sourdough base and sprinkle evenly with grated Parmesan.

7. Drizzle warm lemon butter over the assembled tart and brush exposed bread edges with beaten egg if using.

8. Bake the tart at 400°F (200°C) for 8–10 minutes until the edges are golden and the cheese is melted and crisp.

9. Remove from the oven, let cool briefly on a wire rack, then drizzle with any remaining lemon butter and garnish with fresh herbs before serving.