Although it tastes fine, having cheese curdle in your recipes can be frustrating and it can easily ruin a soup, sauce or fondue. Heat is the culprit when it comes to curdling, but there are steps you can take to keep your melted cheese smooth. A rule of thumb to remember is to add the cheese in last to avoid over-cooking and take the sauce pan off the heat when doing so.
Shred or finely chop up the cheese as it will melt more quickly and smoothly. Let shredded or chopped cheese to sit to become room temperature.
Make a bechamel by melting 3 tbsp. butter in a sauce pan over low heat. Whisk in 3 tbsp. of all-purpose flour and cook, stirring constantly, for a couple of minutes. If you want to make more or less, adjust the amount of butter and flour, but keep them equal amounts.
Add in 2 cups of milk. Increase the heat and cook for about five minutes, whisking occasionally until it is smooth and thickened.
Take the saucepan off the heat and blend in the cheese. Add the cheese in small hand fulls at a time, making sure it is melted before adding in more.
Reduced fat cheese takes longer to melt, do so over very low heat and stir constantly.