Preheat oven to 375°F (190°C).
In a large skillet, melt butter over medium heat.
Add onion, celery, and carrots. Cook until tender.
Stir in flour, salt, pepper, garlic powder, and thyme until well blended.
Gradually stir in broth and milk, cooking and stirring until bubbly and thickened.
Stir in mixed vegetables.
Pour mixture into a baking dish.
Place biscuits on top of the vegetable mixture.
Bake for 20-25 minutes or until biscuits are golden brown.