Cook macaroni in a large pot of salted boiling water until al dente, according to package instructions. During the final 3 minutes of cooking time, add the broccoli florets to the boiling water with the pasta. Drain and set aside.

While the pasta and broccoli are cooking, heat 1 tablespoon of olive oil in a large cast iron skillet or Dutch oven over medium heat. When the oil shimmers, add the sausage rounds and the diced onion. Cook, stirring regularly, until the sausage is browned and the onion is tender, about 5-7 minutes. Remove sausage and onions from the skillet and set aside on a plate. Wipe out the skillet.

Add butter to the skillet and cook, stirring, until the butter melts. Sprinkle in the flour and cook, stirring constantly, for one more minute. Gradually whisk in the half-and-half. Cook and stir until the mixture bubbles and thickens, about 2 minutes. Reduce the heat to low; add the cheddar, gouda, and dry mustard; stir until the cheeses melt. Add cooked macaroni, broccoli, sausage and onion back to the skillet; toss to combine. Garnish with parsley.