In a small saucepan, melt the butter over low heat until it bubbles lightly. Add flour and whisk continuously for about 3 to 4 minutes until it forms a smooth, golden paste.
Slowly pour in the milk, whisking constantly to combine. Increase to medium heat and bring the mixture to a boil until thickened.
Reduce the heat to a gentle simmer, whisking for approximately 5 minutes until you achieve the desired creamy consistency.
Season the sauce with salt, pepper, and, if desired, turmeric and onion powder. Mix well to integrate all flavors before enjoying.