Once melted, add flour and mix until the mixture forms a paste that does not stick to the sides. The quantity of flour required may vary.
Now start adding the milk slowly, while mixing, as to avoid lumps.
Heat on low heat while stirring until the sauce becomes thick. If unsure, taste the sauce, and if you cannot taste the flour, it is ready for the next step.
Add 80% of the cheese and stir until melted in.
Drain the pasta and add to baking dish.
Add the sauce and mix in.
If using bacon, fry it up and mix into the dish, making sure to include any fat that comes out of the bacon for extra flavour.