Preheat the oven to 200°C. Lightly grease a medium-sized ovenproof dish. Cook the macaroni in lightly salted water according to the packet instructions, or until al dente. Drain and rinse under cold water to arrest cooking and set aside.
In a medium-sized, heavy-based saucepan, melt the butter over a low heat then stir in the flour to form a roux. Allow the roux to bubble gently, stirring continuously until lightly golden. Remove from the heat, add hot Half & Half and stir or whisk to combine well. Return to the heat and thicken, stirring continuously.
Add the 1 cup cheese. The cheese will thicken the sauce as well, so add a little more hot Half & Half if too thick.
Stir in the cooked macaroni and season to taste. Spoon into the greased dish and top with the panko crumb and cheese mixture.
Place in the oven and cook for 15-20 minutes until golden and bubbling.