Temper the milk by microwaving it for 45 seconds. This prevents curdling but also prevents lumps from forming when it’s added. Set aside.
Melt the butter in a saucepan over medium heat. Let it fully melt and wait until it starts to foam, about 3 minutes.
Gradually add the flour, whisk continuously for 3-5 minutes, until it’s the consistency of wet sand. Remove from heat.
Add ⅓ of the chicken broth and whisk well. Add ⅓ more, whisk well.
Add the remaining chicken broth, chicken bouillon, warm milk, and seasonings, whisk continuously.
Return to heat and bring to a near boil. Continue to whisk until it begins to get very thick. Immediately remove from heat.
Soup will continue to thicken upon standing.
If possible, run the mixture through a fine mesh strainer for a super-smooth consistency.
