Cook pasta in salted boiling water according to directions on package. Reserve a little pasta water to thin sauce later on if desired. Drain pasta well.
While macaroni is cooking, melt butter in a pot over medium heat. Add in flour and garlic powder and cook, whisking constantly for 2 minutes. Slowly pour in milk while whisking, then once all of the milk has been added whisk somewhat vigorously to smooth any little lumps. Add in cream cheese and mustard and cook, whisking constantly until cream cheese has melted and mixture has thickened well.
Remove from heat then add in cheese and stir briskly to melt cheese. Pour drained pasta and drained broccoli into the pan with the sauce and toss everything to evenly coat, while seasoning with salt to taste. Thin sauce with a little pasta water or milk if desired. Serve warm.
This is 10 oz. florets. It should be mostly the head of the broccoli and little stem. Cook it first until fully tender then chop finely after. You can steam it or boil it in the water for about 4 - 5 minutes then remove before adding in the pasta to boil.
mac and cheese somewhat mild, if you'd prefer a strong flavor feel free to add in more cheddar.