Preheat oven and boil water:
Heat oven to 350°F (175°C). Set a medium pot of water to a boil.Blanch broccoli and onion:
Cook broccoli and onion in the boiling water for 3-4 minutes, then transfer to cold water to halt cooking. Drain thoroughly.Layer vegetables and cheese:
Spread the drained broccoli and onion evenly in the frozen pie crust. Top with an even layer of cheddar cheese.Prepare custard mixture:
In a medium bowl, beat eggs, heavy cream, salt, and pepper until smooth. Pour this custard mixture evenly over the filling.Bake and cool quiche:
Bake without cover for 45-50 minutes, until the center is set and no longer jiggly. Allow to cool for 30 minutes prior to serving.