In a food processor, pulse flour and salt. Add butter and pulse to coarse sand. Drizzle in 4 tablespoons ice water, pulsing until dough just holds together. Press into a disk, wrap, and chill at least 30 minutes.

Preheat oven to 400°F. Roll dough to a 12-inch circle and fit into a 9-inch pie plate. Trim, crimp, and prick bottom. Line with parchment and fill with pie weights. Bake 15 minutes. Remove weights and bake 5 to 7 minutes longer until lightly golden.

On a baking sheet, toss sweet potato cubes with 1 tablespoon oil, salt, and pepper. Roast at 400°F for 20 to 25 minutes, stirring once, until tender and caramelized.

In a skillet over medium heat, warm a drizzle of oil. Add garlic and cook 30 seconds. Add spinach and cook, tossing, until wilted, 2 to 3 minutes. Season with salt. Press out excess moisture.

Lower oven to 375°F. Whisk eggs, half-and-half, 1/2 teaspoon salt, pepper, and nutmeg. Scatter spinach, sweet potatoes, and feta in the crust. Pour custard over and top with Parmesan.

Bake at 375°F for 35 to 40 minutes, until edges are set and center jiggles slightly. Turn oven off, crack door, and cool 10 minutes. Rest on a rack 15 to 20 minutes, then slice and serve.