Prepare the Low-Carb Crust: In a large bowl, whisk together almond flour, coconut flour, psyllium husk powder, and sea salt. Cut in the cold, cubed butter until the mixture resembles coarse crumbs. Add the cold egg and 2 tablespoons of ice water, mixing until a dough forms. Wrap in plastic and refrigerate for 30 minutes.

Blind Bake the Crust: Preheat your oven to 375°F (190°C). Roll out the dough to an 11-inch circle and transfer to a 9-inch tart pan. Trim excess dough, line with parchment paper, and fill with pie weights. Bake for 15 minutes, then remove weights and bake for another 5-7 minutes until lightly golden.

Prepare the Asparagus: Heat olive oil in a frying pan over medium heat. Sauté minced shallot for 2-3 minutes, then add asparagus and cook for 3-5 more minutes. Season lightly with salt and pepper.

Whisk the Filling: In a large bowl, whisk together eggs, heavy cream, Dijon mustard, nutmeg, salt, and black pepper. Stir in the grated Gruyère cheese.

Assemble the Tart: Arrange sautéed asparagus over the bottom of the crust. Pour the egg mixture over the asparagus and sprinkle additional Gruyère on top.

Bake the Asparagus Gruyere Tart: Bake for 30-40 minutes until the filling is set and golden brown. A knife inserted should come out clean.

Cool and Serve: Let cool for 15-20 minutes before removing from the tart pan. Slice and serve warm or at room temperature.