Pour in a little milk, stir with a whisk, breaking the lumps. Pour in the rest of the milk in a thin stream, stirring with a whisk. Add salt (consider the salinity of the cheese! I added one small pinch of salt).
Cook over low heat, stirring with a whisk, until the sauce begins to thicken. As soon as the sauce has started to thicken, remove from the heat.
Add grated cheese and crushed garlic. I preheated the garlic in a small amount of oil. Mix it.
Return to the heat, stir until the sauce is smooth and the cheese is completely melted. Remove from the heat. The sauce is ready.