Boil the water, add a little salt and pasta, cook just until al dent.
Meanwhile in a large saucepan on low / medium heat melt butter, then add the flour and whisk together until smooth, add salt and pepper, then slowly add the milk, stirring to combine. Cook and stir often until the mixture starts to thicken. Remove from heat.
Add shredded cheese and stir until melted, then gently fold in the cooked al dente pasta. Serve immediately topped with some shredded cheese. Enjoy.