For Filling
Preheat oven to 375°F.
In a large skillet or pot, melt butter over medium heat.
Add onion, carrots, and celery. Cook until softened (5–7 minutes).
Stir in flour and cook for 1–2 minutes.
Slowly whisk in chicken broth and milk until smooth.
Simmer until thickened.
Add chicken, peas, thyme, salt, and pepper.
Pour filling into a baking dish.
For Drop Biscuit Topping
In a bowl, mix flour, baking powder, and salt.
Cut in butter until crumbly.
Stir in milk until a thick, scoopable dough forms.
Drop spoonfuls of dough over the filling.
Bake for 25–30 minutes, until biscuits are golden and filling is bubbly.