Preheat your oven to 375°F (190°C). Fit the refrigerated pie crust into a quiche dish, crimp the edges, and prick the bottom with a fork to prevent bubbling. Line the crust with parchment paper, fill it with pie weights or dried beans, and bake for 12–14 minutes. Remove the weights, and bake for an additional 5 minutes until lightly golden. Let it cool while you prepare the filling.

In a large skillet over medium heat, add a splash of olive oil. Once hot, add diced yellow onion and sauté for 4–5 minutes until softened and translucent. Stir in minced garlic and continue cooking for another 30 seconds until fragrant. Add the fresh spinach, cooking for 3–4 minutes until wilted and moisture has evaporated. Remove from heat and allow to cool slightly, then press out any excess liquid.

In a spacious mixing bowl, crack in the large eggs and pour in the whole milk and heavy cream. Whisk together until the mixture is smooth and well combined. Season with sea salt, freshly cracked black pepper, and a hint of ground nutmeg to enhance the flavors.

Spread the cooled spinach mixture evenly over the pre-baked crust. Sprinkle the crumbled feta cheese and shredded mozzarella generously over the spinach. Slowly pour the egg custard over the top, allowing it to fill in the gaps and coat the filling evenly.

Place the assembled quiche on the middle rack of the oven and bake for 35–40 minutes. The edges should puff up and turn golden, while the center should set with a slight wobble. Cover the edges with aluminum foil if they brown too quickly.

Once baked, remove the Spinach And Feta Quiche from the oven and let it rest for 15–20 minutes before slicing. Serve warm, at room temperature, or chilled.