To make this Mac and Cheese with Broccoli gluten free, replace the all-purpose flour with a gluten-free 1:1 flour blend or cornstarch slurry for thickening. Use certified gluten-free elbow or shell pasta and cook it only until tender, as gluten-free pasta can soften quickly. Confirm that the shredded cheese, garlic salt, onion powder, smoked paprika, black pepper, butter, milk, and broccoli are certified gluten free or processed without gluten cross-contamination. Stir gently after adding the pasta, as gluten-free pasta can break more easily.