Preheat oven to 400 degrees.
In a dutch oven or large skillet, melt the butter over medium-high heat. Add the carrots, celery, onion and a pinch of salt. Cook until vegetables are soft, stirring occasionally.
Stir in the flour to coat the vegetables and cook for one minute, stirring constantly. Add half the milk and whisk continually until thickened, about 5 minutes. Repeat with rest of milk. Mix in the chicken soup mix, chicken, peas, thyme and some pepper. Simmer and stir occasionally until chicken is cooked through, about 10-15 minutes. Adjust seasonings as needed.
Carefully pour mixture into a 9x13 casserole dish. Cover top with tater tots. Bake for 30 minutes or until tater tots are golden brown.
Tip: If you have extra tater tots, bake them and serve them to your favorite child. (Joking! Serve them alongside the casserole.)
Cool slightly and enjoy!
