Preheat your oven to 350°F and butter a 9x13-inch baking dish generously. Spread the frozen hashbrowns evenly across the bottom without thawing them first—this prevents a soggy casserole.
In a large mixing bowl, whisk together the eggs, heavy cream, and milk until fully combined. Add the garlic powder, black pepper, salt, and paprika, stirring thoroughly to distribute seasonings evenly throughout the mixture.
Fold in both shredded cheeses and the chopped smoked turkey strips until everything is distributed evenly through the custard. This ensures every bite contains cheese and protein throughout the casserole.
In a separate skillet, melt butter over medium heat and sauté the diced onion and red bell pepper for 3-4 minutes until softened. Add these vegetables to the egg mixture and stir gently to combine while keeping textures intact.
Pour the entire egg and vegetable mixture over the hashbrowns in your prepared dish, spreading it evenly. The summer hashbrown casserole crowd recipe should have the custard covering all the potatoes completely for even cooking and moisture distribution.
In a small bowl, combine the panko breadcrumbs with fresh chives and a pinch of salt. Sprinkle this mixture evenly over the top of the casserole for that signature golden-brown crust.
Bake for 45 minutes until the top is golden brown and a knife inserted in the center comes out mostly clean with just a tiny bit of custard clinging. The casserole will continue cooking slightly from residual heat even after removal from the oven.