Steam the broccoli in a large pot with a steamer basket for around 3 minutes or in a microwave-safe container for 4-5 minutes until soft.
Melt the butter in a small saucepan set over medium heat, then add the onion and cook for 3-4 minutes until translucent. Add the flour and cook for around 1 minute, stirring constantly, until lightly browned.
Add the chicken broth and milk and whisk for 1-2 minutes until the sauce is thickened. Stir in 1 cup of cheese, sour cream, salt, pepper, onion powder, garlic powder, mustard powder, and paprika.
Spread the broccoli into an even layer in a baking dish, then add the chicken. Pour the sauce over the top of the broccoli and chicken, then top with the remaining cheese and the crushed crackers.
Cover with foil and bake for 15 minutes, then remove the foil and bake for another 8-10 minutes until the topping is browned and the sauce is bubbling. Let cool for 5 minutes before serving.
Notes
Store leftovers in an airtight container and refrigerate for up to 4 days. You can also freeze the leftovers for up to 3 months. If freezing, thaw in the fridge overnight before reheating.To reheat, place the leftovers in a baking dish and cover with foil. Then, bake in a 325°F oven for 10-12 minutes until warmed through.