Fill a medium sized saucepan with water for cooking macaroni. Turn on heat to high. When it boils, add macaroni and cook according to package directions. Do NOT overcook the macaroni!
Meanwhile, begin cubing the cheese. Melt butter in a skillet. Add flour and stir to make a roux. Add 1 1/4 cups milk and stir, cooking on medium heat, to thicken. Add cheese cubes. Stir until melted and sauce is smooth. You can add a little extra milk if you think it is necessary. Combine the cheese and cooked macaroni. It may seem a little thin at first, but if you let it sit for 5 minutes, the macaroni will absorb a lot of the liquid and it will be a nice consistency.