Preheat the oven to 480°F.
Add 18 oz worth of chopped cauliflower to a bowl and cover with plastic wrap. Microwave for 7 minutes. Alternatively, you can boil or steam it instead.
Meanwhile, heat a non-stick pan or skillet over medium heat. Stir together 1/2 tbsp olive oil, 1/2 tbsp unsalted butter, and 3 tbsp all-purpose flour for about 30 seconds.
Add 1 cup chicken broth gradually and constantly (but gently) stir as you go to incorporate the flour. Add 1/4 cup whole milk and mix everything together. Season it with 1 tsp garlic powder, 1/4 tsp pepper, and 1/4 tsp salt, and allow the mixture to come to a boil. Once it does, turn off the heat and stir in 1 tbsp heavy cream.
Wait for the cauliflower to finish cooking, then transfer it to a baking dish. Pour in the sauce and give everything a gentle toss to coat.
Sprinkle 1/4 cup breadcrumbs and 1 oz shredded cheddar on top, and slide the baking dish into the preheated oven to cook for 15 minutes.
Sprinkle 2 tbsp chopped parsley on top and serve.