Melt the butter over medium-high heat in a medium-sized saucepan.
Whisk the flour and garlic powder (if using) into the butter until fully incorporated and smooth.
Slowly whisk in the milk while cooking, stirring frequently over medium-high heat. Allow the mixture to thicken for about six minutes.
Season the mixture with salt and white pepper to taste.
Add the frozen peas to the sauce, stirring constantly until heated through.
If desired, stir in the heavy cream for extra richness.
Check the seasonings one final time.
Garnish with additional pepper, a pat of butter, and fresh chopped herbs before serving.
