- Melt butter in a skillet over medium heat; add onion and cook for 1 minute. Add spinach and cook, stirring occasionally, until starting to wilt, about 1 minute. Cover skillet and cook for 1 minute more, allowing condensation to build inside the skillet. Remove from heat, uncover, and stir.
- Preheat the oven to 375 degrees F (190 degrees C). Press pie pastry into a 9 1/2-inch deep-dish pie pan. Prick bottom and sides with a fork.
- Bake crust in the preheated oven for 10 minutes. Remove from oven and set aside.
- Combine eggs, ricotta cheese, cream, Parmigiano Reggiano cheese, basil, salt, and pepper in a blender or food processor. Blend until smooth.
- Spread spinach and onion mixture evenly over the crust. Pour egg mixture on top.
- Bake in the preheated oven until center of quiche is set and the top is lightly browned, about 40 minutes. Allow to stand for 10 minutes before serving.