1 Bring a large pot of water to a boil.
2 Meanwhile, cut the cauliflower into bite-size pieces.
3 Add the pasta to the boiling water and cook until al dente, 10 to 12 minutes, or according to package directions. Add the cauliflower to the pasta water 5 minutes before the pasta is done.
4 Meanwhile, in a medium saucepan, melt the butter over medium heat. Add the garlic and cook for 1 minute.
5 Stirring constantly, add the flour and cook until the flour absorbs all the butter. Then slowly pour in the chicken broth and stir until smooth.
6 Blend in the milk, Cheddar, mustard and pepper, and stiruntil the cheese is melted.
7 Drain the pasta and cauliflower and toss them with the cheese sauce.