Preheat oven to 425°. Unroll pie dough into a 9-in. pie pan. Crimp edge. Line dough with parchment paper, fill with pie weights or dried beans, and bake until light golden, about 15 minutes. Remove paper and weights.
Melt butter in a large frying pan over medium heat. Add leeks, green and red onions, and 1/2 tsp. salt. Sauté until very tender but not browned, about 20 minutes.
Whisk half-and-half gradually into flour in a medium bowl until smooth. Whisk in remaining 1/2 tsp. salt and eggs until blended. Stir in cheese and three-quarters of onion mixture and pour into pie shell. Sprinkle remaining onions over quiche.
Bake until a knife inserted in center comes out clean, 20 to 30 minutes; cover edges with foil if they begin to darken. Let sit 10 minutes, then cut into wedges.
*We especially like Pillsbury pie dough. Look for Beecher's Flagship cheddar cheese sold at specialty shops.
Note: Nutritional analysis is per serving.