Make the filling: in a large pan, heat the olive oil. Add the diced butternut squash, leeks, pancetta, salt, black pepper and red pepper. Sauté the vegetables until the butternut squash is soft and the leeks are translucent.
Make the crust: in a medium bowl, use a spatula and stir together the paleo flour, arrowroot and salt.
Add in the olive oil, water and egg. Mix until thoroughly combined. Pour the dough onto a work surface lightly dusted with the flour. Gently shape the dough into a disk that’s 1 inch thick. Wrap with plastic wrap and place in the fridge for 1 hour, or overnight.
Preheat the oven to 375°F. Remove the dough from the fridge and place on parchment paper or a silpat that has been dusted with flour. Using a rolling pin, roll the dough to roughly an 11-inch circle that’s 1/4-inch thick.
Place the butternut squash filling in the middle of the dough, leaving 2 inches of space between the filling and the edges of the dough. Fold the edges of the dough inwards, overlapping. Note: this dough is very delicate and will crack as you’re working with it. If so, just patch together the edges with little pinches–it’s a rustic galette, so that’s okay!
Transfer the parchment (or silpat) with the dough onto a baking tray. Brush the edge of the galette with the egg. Sprinkle the crust and center of the galette with the flake salt and black pepper. Bake for 20-25 minutes until the crust is golden brown. Cut into four equal pieces and serve immediately.