Many viewers have asked me this question and believe me I myself too initially had this problem while preparing white sauce. There are two simple tricks.
1. Always use cold milk.
2. Let the flour cool down before you add milk.
Follow the following recipe and you will never have lumps in your white sauce.
Basic White Sauce
Ingredients:
1 tbsp butter,
3-4 tbsp all-purpose flour or wheat flour,
2 cups cold milk,
Salt and Pepper to taste.
Method:
Melt butter in a heavy bottom saucepan. To that add flour and lightly roast on low-medium flame till it is fragrant. Do not burn. Then remove it from flame and let it cool down completely. To that add cold milk. Mix with a whisk to get a even mixture. Return to flame, keep the flame on low and cook stirring continuously till it thickens (but pouring consistency). Season it with salt and pepper while cooking.
Serving Suggestions:
Use this white sauce on baked vegetables, pastas or soups.
TIP:
Try these variations-
1. Add some chilli flakes
2. Season with some oregano to taste.
3. You can also add some mustard paste/sauce.
4. Add generous amount of cheese to use it with baked vegetables and pastas.