Preheat the oven to 355F (180C) and prepare a 9-inch (23cm) pie dish.

In a food processor, pulse to combine the almond flour, coconut flour, psyllium husk powder, xanthan gum, and salt.

Add the cubed butter and pulse to combine again until the mixture resembles wet sand.

Add the egg and pulse one last time until the mixture comes together and forms a ball. With your hands, form a round disk from the dough, wrap it in plastic wrap, and freeze for 15 minutes.

When the dough is cold but still pliable, roll it out between a piece of parchment paper on the bottom and plastic wrap on the top until it’s around 0.15 inches (4 mm) thick. Then, flip and remove the paper and lift the rolled dough on the plastic wrap. Carefully flip it onto the pie dish and gently push dough inside the pan corners without removing the plastic wrap. Remove the wrap, fix all the cracks (if they appeared), and even out the crust. Freeze for 10 minutes before baking.

When the crust has firmed a little bit in the freezer, take the pan out and bake on a lower rack for 8 minutes or until the crust starts picking up a golden color in the middle.

When done, remove from the oven, let it cool a little bit, and gently press down with a spoon or the flat bottom of a cup if the crust has puffed up.

Keep the oven running at 355F (180C).

While the crust is cooling down, heat a frying pan with some olive oil over a medium heat. When hot, add onions, season with salt and pepper, and cook until just golden. When done, remove into a large mixing bowl.

Add the chicken, eggs, cheese, and heavy cream. Season with salt and pepper to taste and mix well until the eggs reach a homogenous consistency.

Pour the mixture into the warm pie crust, top with tomato halves (optional), and sprinkle with additional shredded cheese.

Bake for around 30 minutes or until the filling has set and is slightly jiggly. If the crust starts browning too much, cover the edges of the crust with a pie shield or strips of aluminum foil and continue baking. Remove from the oven and leave to cool down until warm. Then, slice and serve.