Cook spaghetti by adding boiling water and a pinch of salt to a pot.
On a heated sautéing pan, add butter. Once melted, add flour and whisk until the roux develops a golden brown color.
Reduce the heat and start slowing adding the milk while whisking vigorously this time. Continue whisking until the white sauce is smooth and bump-free.
Add grated cheese and a dash of salt and pepper to taste.
Combine the cheese sauce with the spaghetti and plate. Garnish with more cheese and serve warm.