Saute 1/4 cup each of diced carrot, celery and onion in 1 tbsp. of butter for about 5 minutes or till softened. Add 1 tsp dried thyme during last couple minutes.
Rinse chicken and dry with paper towels inside and out. Season inside with salt and pepper. Toss sauteed vegetables with 8 thin lemon slices and spoon into cavity. Truss chicken. Here’s a nice method: https://www.youtube.com/watch?v=Gs1zHP7oabM. Rub outside with butter and season with salt and pepper.
Roast breast side up at 425 degrees for 15 minutes. Brush with a little more butter. Turn heat down to 350 degrees and roast another 45 minutes then drizzle with juice from 1/2 lemon . Continue roasting a total of 20 minutes per pound – 2 hours for a 6 pound chicken.