Prepare Tart Dough: In a food processor, combine flour and kosher salt. Cut in cold butter until the mixture resembles coarse crumbs, about 30 seconds. Gradually add ice-cold water, pulsing until the dough just comes together. Shape the dough into a disk, wrap it in plastic wrap, and chill in the fridge for at least 1 hour for optimal flakiness.

Wash Dandelion Greens: While the dough chills, rinse the dandelion greens thoroughly under cold running water to remove any dirt or grit. Pat them dry with a clean kitchen towel and chop into bite-sized pieces.

Sauté Vegetables: Heat a skillet over medium heat and add a mixture of olive oil and butter. Once the butter melts, add diced onion and sauté for about 5 minutes, stirring until the onion becomes translucent. Add minced garlic and cook for another minute until fragrant.

Cook Greens: Add the chopped dandelion greens to the skillet, tossing them in the hot oil mixture. Cook until wilted, about 3-5 minutes. Incorporate the lemon zest, stirring until combined.

Mix Filling: In a mixing bowl, whisk together the eggs, heavy cream, and a pinch of salt and pepper until smooth.

Assemble Tart: Preheat your oven to 400°F (200°C). Roll out the chilled dough to fit your tart pan. Press the dough into the pan, dock the bottom with a fork, and blind bake for 15 minutes until lightly golden. Layer the sautéed greens evenly on top, crumble feta cheese over it, and pour the cream mixture.

Bake Tart: Sprinkle shredded Parmesan cheese on top of your tart filling. Bake for 35-45 minutes, or until golden brown and the filling is set. Let cool slightly before serving.