1. Preheat the oven to 375F. Then add butter to a saucepan and cook the onions til soft (around 20 mins).
2. Add the flour and stir well until you have a smooth-like paste. Slowly add in the milk and whisk continuously. Once the milk has been blended in, simmer for a bit then whisk in the garlic, mustard, and thyme. (If needed, add some pasta water to make it smooth or not too clumpy-like)
3. Cook your pasta and around the 5 min mark before draining, add your broccoli florets. Let them cook and drain. Transfer to a casserole dish.
4. Add the sauce over the broccoli and pasta. Top it off with the breadcrumbs, more cheese and parsley. Cover with tin foil and pop it in the oven for 20-25 mins.
5. OPTIONAL: The Last Food Blog grilled hers for 10 mins for a crunchy coating. We didn't have a grill so we settled for more of a soft texture. Either works!