In a large pot, melt 1 1/2 Tbsp butter over medium heat. Add onion, carrot, and celery and saute until tender, about 4 minutes. Add chicken broth, potatoes, oregano, thyme, and bay leaf and season with salt and pepper to taste*.
Meanwhile, in a medium saucepan, melt remaining 4 Tbsp butter over medium heat. Add flour and cook mixture, stirring constantly, 1 1/2 minutes.