Take a NON STICK pan, put it on the stove and light the stove at medium flame, let the pan heat.
Add some butter, let it melt down, and turn into a liquid.
After the butter is melted, add the same amount of flour as the butter to the pan
Whisk the mixture until the flour turns into a light golden paste. Cooking the flour with butter makes a paste called a roux. Roux is the base of our sauce.
Start pouring milk slowly into the paste. Also, continue whisking while adding milk. Whisking will prevent the lumps from forming.
Continue stirring the paste until you get a creamy paste
Once the sauce is thickened, turn the heat down.
Start with adding the cheese slowly and continue with stirring.
Add some spices like salt, pepper, cayenne, and voila.
Your perfect cheese sauce is ready to serve over fries