Heat oven to 350 degrees. Cook macaroni as package directs (plus dash of salt in water), decreasing time to 3 minutes; drain. In medium saucepan over medium-low heat, melt margarine. Slowly blend flour and pepper in 1 cup milk, using whisk. Add the rest of the milk periodically so the mixture doesn’t become lumpy. Gradually add milk to butter in saucepan, whisking, and cook until mixture is smooth and bubbly. Cook and stir periodically over medium heat until mixture starts to thicken. Gradually stir in cheese. Cook and stir over low heat until cheese in melted. Add pasta, mix lightly. Pour into casserole dish. Bake 25 minutes.