Melt the butter in a large saucepan over medium heat with the pressed garlic.
Add the flour, mix with a whisk and cook the roux for about 3 to 5 minutes, stirring.
Pour in the milk (all at once), mix over medium heat, then cook until the sauce thickens.It should be very thick.Remove from the heat, salt lightly or not (as there will be cheese), pepper and sprinkle with a little nutmeg. Mix well. Add the grated cheese and mix again until well incorporated.