Preheat your oven to 400°F (200°C).
In a large oven-safe skillet or sauté pan, melt the butter over medium heat. Add the onion and garlic, cooking until softened.
Stir in the flour and cook for 1 minute to form a roux. Gradually whisk in the broth and milk, cooking until thickened.
Season with thyme, salt, and pepper. Add the frozen vegetables and simmer for 5 minutes.
Remove from heat and top the mixture with biscuit dough.
Transfer the skillet to the oven and bake for 15–18 minutes, or until the biscuits are golden brown and cooked through.
Let cool slightly before serving.