Preheat oven to 400˚F and lightly grease a 9×13 baking dish; set aside.
Add water to a large pot, filling it about halfway up, and bring to a boil.
Add broccoli florets and cauliflower florets to the boiling water; bring to a boil and continue to cook for 3 minutes. Drain well and set aside.
In the meantime, add the vegetable oil to a skillet and heat over medium-high heat. Stir in the onions and cook for 2 minutes; add the garlic and cook for 15 seconds.
Then, stir in the smoked sausage and cook for 3 minutes or until browned on all sides. Stir frequently.
Transfer the broccoli, cauliflower, plus sausage mixture to the baking dish.
In a mixing bowl, combine cream cheese, mayonnaise, 1 cup shredded cheese, Dijon mustard, salt, and pepper; mix until thoroughly incorporated.
Stir the cream cheese mixture into the broccoli mixture; stir around until everything is well combined. Add remaining shredded cheese on top.
Bake for 12 to 15 minutes, or until cheese is melted and top is golden brown.
Remove from oven and serve.
Prep Time: 15 minutes | Cooking Time: 15 minutes | Total Time: 30 minutes
Kcal: 400 kcal | Servings: 6 servings