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 shaped biscuits on a lined plate or baking pan, cover tightly, and refrigerate until ready to use.

Melt the butter in a large skillet over medium heat. Add the onion, carrots, celery, mushrooms, and garlic. Cook for 5 minutes or until vegetables have softened. Stir in flour, salt, pepper, and thyme until flour absorbs all the liquid. Stir in the broth and ½ cup milk. Simmer for 7–9 minutes until thickened. Stir in mixed vegetables and parsley, then remove from heat.

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 increase oven temperature to 425°F (218°C) and bake for 5–6 more minutes until biscuits are golden.

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