In a large casserole set over medium-low heat, sauté the onion and garlic in butter for 5 minutes. Add the flour and continue to cook 1 minute. Add the broth and cook for 5 minutes, stirring frequently.
Add the ham, rosemary, and milk and bring to a low boil. Add the penne and stir to combine. Season, stir, and continue to cook 10 minutes, stirring halfway. Add the green peas, stir, and continue to cook 2 minutes.
Add 250 ml of the Armstrong Triple Cheddar shredded cheese and stir until cheese has melted. Serve and garnish with the remaining shredded cheese.