Cook the pasta in a large saucepan of salted boiling water for 8 minutes. Add the cauliflower. Cook for 4 minutes or until pasta is al dente and cauliflower is tender. Drain and return to the pan.
Meanwhile, melt the butter in a saucepan over medium-high heat. Add bacon, onion and garlic and cook, stirring, for 2-3 minutes or until the onion softens. Whisk in cream cheese, milk and mustard. Season with salt and pepper.
Preheat grill on high. Combine 40g (1/2 cup) cheddar and half the parsley in a bowl. Add bacon mixture, remaining cheddar and remaining parsley to the pasta mixture. Stir to combine. Transfer to a 2.5L (10-cup) capacity baking dish. Top with parsley mixture. Cook under grill for 5 minutes or until cheddar melts. Serve.
Store, covered, in the fridge. Preheat oven to 180C. Bake for 30 minutes or until heated through and cheddar melts. On the side, try a rocket and tomato salad with balsamic vinegar dressing.
Variation: For Macaroni bake with broccoli and blue cheese, omit the bacon. Replace the cauliflower with broccoli. Replace the cheddar with blue cheese.