Preheat oven to 360 F (180 C).
Grease a 9.5 inches (24 cm) round quiche ceramic dish with butter or coconut oil. I used this kind of Round Quiche Dish, 9.5 by 1.5-Inch, border. Set aside.
In a frying pan, under medium heat warm the olive oil.
Add garlic and onion. Fry until fragrant and golden brown. Stir often to avoid the spices to burn.
Add the frozen spinach cover and reduce to low heat. Cook until the spinach are cooked through, soft and tender - about 15 minutes. Adjust with salt and pepper regarding taste.
Meanwhile peel the sweet potatoes then use a mandoline Vegetable Slicer to finely slice the sweet potatoes.
Arrange the slices on the pan making sure that you cover all the bottom leaving no empty space. For the border, cut in half the sweet potatoes slices to create a 'flat' bottom it will hold better and create a beautiful crust border.
Prebake the sweet potato crust at 180C for 15 minutes. This is optional, you can also add the spinach and egg filling directly and bake your quiche - make sure you cover the dish with a piece of foil to ensure the quiche is cooking at the same speed. I prefer to prebake the crust to avoid foil - up to you.
Spread the cooked spinach all over the pre baked sweet potatoes crust. Set aside.
In a medium mixing bowl beat the eggs, almond milk and nutmeg. Adjust with salt and pepper if desired,.
Pour the egg mixture onto the quiche..
Add an handful of grated cheese on the top of the quiche, if desired. If paleo, sprinkle almond meal on top instead of cheese, it give a delicious crisp on top.
Bake for 25-30 minutes or until the sweet potatoes are soft and the cheese is grilled.