Preheat the oven to 350°F (175°C) and grease a 9x9-inch baking dish.

In a large skillet over medium-high heat, brown the sausage slices for about 5–7 minutes, then remove and set aside.

Melt the butter in a saucepan over medium heat, add the diced onion, and cook until softened, about 3–4 minutes.

Stir in the garlic and cook for another 30 seconds.

Lower the heat, add the softened cream cheese, and stir until melted. Whisk in the heavy cream and simmer for 3–5 minutes until the sauce thickens.

Remove from heat and fold in shredded cheddar until smooth; season with salt and pepper.

In a large bowl, combine broccoli and cauliflower florets with the browned sausage, then pour the cheese sauce over and toss to coat.

Transfer to the prepared baking dish and bake for 15–20 minutes until bubbling and lightly golden.

For extra browning, broil for 1–2 minutes.

Let rest for a few minutes before serving.