Melt the butter in a medium saucepan over low heat. Add the flour and whisk quickly until smooth. Continue to cook this flour mixture over low heat for 2-3 minutes, whisking constantly. This is important so that the sauce doesn't taste like flour.
Add ¼ cup of the milk and whisk until all of the lumps are gone.
Add another ½ cup of milk and whisk until smooth.
Then add the remaining milk. Cook and stir over medium-low heat until the mixture starts steaming and thickening. This will take 3-5 minutes.
Once the mixture has thickened slightly, remove the pan from the stovetop and add the cheese in ¼ cup increments and mix until melted and smooth. Please note: the milk mixture should be hot enough to remove from the stovetop and still melt the cheese in. If not, put it back on the warm burner, but have the heat off. This will help prevent the cheese from separating.
Up to ½ teaspoon of salt, especially if butter is unsalted and veggies are unsalted that you are putting it on.Refer to the article above for more tips and tricks.The calories shown are based on the recipe serving 10, with 1 serving being 1/10 of the sauce. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**