Heat the oven to 425 degrees. Prick the pie crust with a fork around the bottom and sides. Place a piece of foil covering the bottom inside of the pie and place pie weights or dry beans on the foil. Bake for 12 minutes then remove and place on a baking sheet. Set aside.
Lower the oven temperature to 350 degrees.
Blanching the green asparagus and Romanesco: Bring a large pot of water to a boil. While the water is heating. Fill a large mixing bowl with cold water and ice. Blanching the green asparagus and romanesco will both soften them slightly but will preserve their green color in the baking process.
Once the water is boiling place the green asparagus and romanesco in the water for 1 minutes only. With a slotted spoon scoop the vegetables out of the hot water, allowing excess water to briefly drain and place them in the ice bath to stop the cooking process. When the vegetables are cool to the touch remove them and place them on a kitchen or paper towel to drain.
Heat a large skillet over medium-high heat. Melt butter. Add leeks to the pan; stir frequently for 3 minutes or until the leeks begin to soften and turn translucent.
Add both asparagus and romances to the skillet. Sauté and additional two minutes. Remove from heat.
In a medium mixing bowl combine the lightly beaten eggs, half and half, salt, pepper, mustard and mix to fully combine. Add the grated cheese and stir to combine.
Place the pre-baked pie crust on a baking sheet. Scoop the prepared vegetables into the pre-baked pie crust, evenly distributing them.
Pour or spoon the liquid mixture over the vegetables ensuring even distribution in the pie pan.
Place the quiche in the oven and bake 30-40 minutes until golden brown on top and the middle is set (a knife inserted will come out clean and it will be firm if the quiche is moved). Remove from oven and allow to rest for 15-20 minutes before slicing.