Drain excess moisture thoroughly from the thawed hash browns using a clean kitchen towel or paper towels. Transfer to a mixing bowl and combine with grated cheddar, salt, and pepper. Mix until well incorporated.
Lightly coat a 9-inch springform pan with non-stick spray. Press the hash brown mixture into the base and up the sides of the pan, ensuring there are no gaps or holes. This forms the crust and prevents leakage during baking.
Transfer the prepared pan to the freezer and chill for a minimum of 1 hour.
Preheat the oven to 425°F (218°C). Take the frozen crust from the freezer and place it directly into the oven. Bake for 15 minutes to partially cook the base. Remove and let it cool slightly.
Meanwhile, in a sauté pan set over medium heat, melt the butter. Add the onion slices and cook, stirring occasionally, until golden and softened, approximately 10 to 15 minutes. Season lightly with salt and pepper, then set aside to cool.
In a large bowl, whisk together the eggs and cream until light and smooth. Stir in the caramelized onions, crumbled bacon, grated cheddar, and chopped chives. Season to taste with salt and pepper.
Pour the egg mixture into the pre-baked crust, smoothing the top evenly.
Reduce oven heat to 375°F (190°C). Return the pan to the oven and bake for 25 to 30 minutes, or until the center is just set and no longer jiggles.
Carefully remove the pan and run a small knife along the inner edge to loosen the crust. Detach the springform collar and place the quiche back in the oven for an additional 10 to 15 minutes, allowing the sides to crisp fully.
Let the quiche rest at room temperature for about 10 minutes before slicing. Garnish with extra chives and serve warm.