Roast the butternut squash: In a large bowl, toss the cubed butternut squash with 1 teaspoon of the olive oil, salt and pepper. Spread out evenly on a baking sheet lined with parchment paper. Roast at 425°F for 15-20 minutes, until tender. Remove and set aside. Reduce oven to 375°F. If baking in a cast-iron skillet, proceed to the next step. Otherwise, lightly grease an 8”-9” pie pan.
Sauté the veg: Warm 1 tablespoon olive oil in an 8-9” cast-iron (or regular) skillet over medium-high heat. Add leeks and garlic, and sauté until tender. Stir regularly to keep the garlic from burning. Turn off the heat and add in the shredded potato and chopped parsley. Stir to combine everything, seasoning well with salt and pepper. If your skillet is not oven-safe, transfer the mixture to your prepared baking dish.
Add the JUST Egg: Shake the JUST Egg well and pour over the sautéed mixture. Shimmy the pan to make sure everything settles evenly. Sprinkle the top with the roasted butternut squash cubes. Season with salt and pepper.
Bake and serve: Bake at 375°F for 30-40 minutes (see note), or until the liquid in the center is set. Let sit for at least 10 minutes before slicing and serving. Run a paring knife around the edge of the frittata to help loosen it from the pan. This frittata is delicious both warm and at room temperature. It will keep for 3-4 days in the fridge if covered tightly.