Heat 2 tablespoons of butter in a skillet over medium heat. Once it has melted and is beginning to bubble, add the onions, mushrooms, and garlic. Sauté for 6 to 7 minutes or until the onions are soft and creamy.
In a large bowl, whisk the eggs, parmesan cheese, gruyere cheese, and french cream until smooth.
Place a layer of kale on the bottom of the crust. Spread the sautéed onions, mushroom, and garlic on top of the kale. Sprinkle the rest of the kale on top. Pour the egg mixture into the tart pan. Because there is so much kale, you might have to jiggle and get your hands in there to make sure the egg mixture is spread evenly throughout the pie tart pan.
Top with a sprinkling of gruyere and then parmesan cheese. Put in the oven and bake for 30-35 minutes.