1. Preheat oven to 375 degrees F. Lightly spray a 9-inch pie pan with olive oil or vegetable cooking spray.
2. Prepare the crust. Grate sweet potatoes into a large bowl using the widest holes on a box grater. Stir in flour, kosher salt, 1/4 tsp. black pepper, and cayenne. Mix well, then add beaten egg and mix well to make sure it's evenly distributed. Transfer to prepared pie pan and press firmly against bottom of pan and up along the sides. Spray surface with cooking spray. Bake for 30 to 35 minutes, or until crust is fairly dry and edges are lightly browned.
3. While the crust bakes, prepare the filling. Place spinach in a microwave-safe bowl, cover with paper towels, and microwave on high for 1 minute. Stir, then microwave on high for another minute. Spinach should becooked and wilted; if it is not yet wilted, cook for additional 30-second intervals until it is. Drain cooked spinach in a strainer, pressing out any extra liquid with the back of a spoon. Finely chop, then spread over cooked crust. Sprinkle with feta cheese.
4. In a medium bowl, lightly whisk the 4 eggs. Gently whisk in milk, nutmeg, 18 tsp. salt, and 1/2 tsp. pepper and pour over spinach mixture. Bake for 35 minutes or until middle of tart feels firm and a toothpick inserted comes out dry. Let sit for 10 minutes before cutting. Serve hot.
Source: Fresh Magazine March, April 2010