Preheat your oven to 400°F. Lightly grease a 9x13 pan.
Fill a large saucepan with water, and bring to a boil. Stir in the macaroni and the cauliflower together; cook until al dente, about 8 minutes. Drain well, and transfer the macaroni and cauliflower into prepared 9x13 pan.
Wipe the saucepan, then melt butter over medium heat. Add flour, ground mustard, salt and garlic powder; and stir to combine. Add milk and whisk with the flour mixture until smooth and thick, about 4-5 minutes. Reduce heat to low, add the cheese and stir to combine.
Pour the sauce over the macaroni and cauliflower and stir to combine. Bake, uncovered until it sets, about 10 minutes.
Storage: Store any leftovers in an airtight container. They will last about 3-4 days in the fridge.Substitutes: For best results, follow the recipe as is. However here are some common substitutes that would work well in this recipe.
Use other types of shredded cheese in place of white cheddar if you'd prefer.
Instead of milk, you can use dairy-free milk like unsweetened almond milk.
Instead of butter, you can use olive oil
To make it gluten-free, you can use almond flour or a GF 1:1 mix. Here's an excellent post on how to make gluten-free roux. You can also make this with gluten-free pasta.
Nutritional Data: The information below is an automated estimate and could vary based on cooking methods and ingredients used. It's estimated for 2 ounces of pasta per person.