In a food processor, pulse flour and salt until combined. Add cold butter and pulse to resemble coarse crumbs. Gradually mix in ice-cold water until dough forms. Chill for at least 1 hour.

Wash dandelion greens under cold water, pat dry, chop coarsely, and set aside.

Heat olive oil and butter in a skillet. Sauté onion until tender, add garlic, then dandelion greens, and cook until wilted. Stir in lemon zest and let cool.

Whisk eggs, heavy cream, salt, and pepper until smooth.

Preheat oven to 400°F (200°C). Roll out dough, fit into tart pan. Bake crust for 15 minutes. Fill with sautéed greens, crumble feta, pour egg mixture, sprinkle parmesan, and bake for 35-45 minutes until set.

Cool for 10-15 minutes before slicing and serving.