1-First Step: Mise en place and crust prep
Preheat the oven to 350°F. Let the pie dough reach room temperature so it rolls easily. Roll the dough into a 12-inch diameter circle, then transfer it gently to a 9-inch deep pie dish. Press the dough into the bottom and up the sides, trimming excess with about a 1/2-inch overhang. Fold or crimp the edges to seal. Prick the bottom of the crust several times with a fork to vent steam, then place the pie dish on a small baking sheet for easy handling.

Par-bake the crust: bake for 10 to 15 minutes until partially set and slightly golden. This par-bake seals the crust to prevent a soggy bottom once the zucchini and custard are added. Remove from the oven and set aside while you make the filling.

2-Second Step: Sauté the vegetables
Heat 1 tablespoon olive oil in a skillet over medium heat. Add 1/4 cup diced red onion and sauté with the minced garlic for about 30 seconds until fragrant. Add the thinly sliced zucchini, 1/2 teaspoon salt, and freshly ground black pepper to taste. Cook the zucchini for 7 to 8 minutes, stirring occasionally, until the slices soften and most of the water releases. Cooking first removes excess moisture that would otherwise make the quiche soggy and concentrates the zucchini flavor.

Using a slotted spoon, transfer about three-quarters of the sautéed zucchini to the par-baked crust, spreading it into an even layer. Reserve the remaining zucchini for the top of the quiche.

3-Third Step: Make the egg and cheese custard
In a mixing bowl, whisk together 6 large eggs and 1/2 cup skim milk until blended. Add 1/2 cup part-skim ricotta, 1/2 cup part-skim shredded mozzarella, 2 tablespoons of the grated Parmesan, 2 tablespoons chopped basil, and salt and pepper to taste. Whisk until smooth and evenly combined. The ricotta adds creaminess while the mozzarella keeps a melty texture; Parmesan brings savory depth.

Pour the egg and cheese mixture evenly over the zucchini layer in the par-baked crust. This ensures the custard settles around the vegetable pieces for an even bake.

4-Fourth Step: Finish assembly and bake
Top the quiche with the reserved zucchini slices and sprinkle the remaining 2 tablespoons of Parmesan over the top. Cover the crust edges with foil to prevent over-browning. Place the quiche on the baking sheet and bake at 350°F for 50 to 60 minutes. The quiche is done when the eggs are set and the top is lightly browned; the center should not be jiggly.

Cool the quiche on a wire rack for at least 10 minutes before slicing into 6 slices. Garnish with extra chopped basil and serve warm or at room temperature. This brief rest helps the custard finish setting and gives cleaner slices.