Filling: Preheat oven to 400 degrees F. In glass baking pan with sides, toss cauliflower with 4 tablespoons of olive oil and sprinkle with salt and pepper to taste. If necessary use 2 pans. Roast about 40 mins, turning in the pan every ten mins, until cauliflower is softened and starting to turn light brown. Set cauliflower aside. In a thick, wide-bottomed sauté pan melt 3 tablespoons of butter and add the onions. Salt to taste. Cook the onions over medium low heat (sweating them) stirring about every 20 minutes until the onions are honey colored. Add 2 minced garlic cloves and sauté over medium heat. Add yu-choi, 1/8 teaspoon of cayenne, salt and pepper to taste and toss. Put tight fitting lid on pan and cook until yu-choi is soft. Squeeze extra liquid out of chard and set aside. Now we make the sauce. Whisk 3 eggs together in bowl, add heavy cream, half the cheese, 1/4 teaspoon ground nutmeg, dash of pepper. Stir together and set aside. Filling the crust. I used a pre-bought pie crust to save time. The original recipe for a flaky cheese crust is below and sounds yummy. Spoon in the onions and yu-choi. Add the roasted cauliflower. Pour on the sauce. Cover with the remaining cheese. Bake at 350 degrees F for 40 - 45 minutes until tart is bubbling and brown. Transfer to rack and cool 15 minutes before serving. Tart Crust: In food processor pulse flour and salt together. Then add 10 tablespoons of cut butter and pulse for about 10 seconds until mixture looks like corn meal. Add Parmesan cheese, cayenne pepper and nutmeg and pulse several times until mixed. Put dough in medium bowl, add water and using a wooden spoon or spatula gradually gather the mixture into a ball adding water as needed. Make the ball into a disk and wrap in plastic and freeze the dough for 10 minutes or chill it in fridge for 30 minutes. Roll out dough on floured surface and when large enough and about 1/4 " thick place in pie or tart pan, crimp edges and put back in the freezer for 10 minutes. Take dough out of freezer, line it with tin foil or parchment paper, weight the bottom with pie weights or dried beans. Bake at 400 degrees F for 12 minutes. Remove from oven and carefully remove weights and foil or parchment paper. Turn oven to 325 degrees F and bake for another 20 minutes or until done. Take out of oven.