Whisk the flour, baking powder, and salt together in a large bowl or use a food processor. Add the cold butter and cut into the dry ingredients with a pastry cutter or pulse several times in the processor. Cut/pulse until coarse crumbs form. Add 1 cup (240ml) milk, and then stir/pulse until the dough comes together.

Shape biscuit dough into 8 or 9 1-inch-thick discs. Place formed biscuits on a lined plate or baking pan, cover tightly, and refrigerate until ready to use, or for up to 2 days.

Melt the butter in a large skillet over medium heat. Add the onion, carrots, celery, mushrooms, and garlic. Cook for 5 minutes until vegetables have softened.

Stir in flour, salt, pepper, and thyme until flour has absorbed all the liquid. Stir in the broth and ½ cup milk. Cook and simmer for 7–9 minutes until thickened into a soup-like consistency.

Stir in the mixed vegetables and parsley, remove from heat, and cool for 5 minutes.

Preheat oven to 400°F (204°C). Pour filling into a greased baking dish. Arrange cold biscuits on top and brush with remaining 2 tablespoons milk.

Bake for 25 minutes, then raise oven temperature to 425°F (218°C) and bake for another 5–6 minutes, until biscuits are golden brown.

Remove from oven and allow to cool for 5 minutes before serving.