Preheat oven to 400 degrees F and grease baking sheet with cooking spray. Place biscuit mix in large mixing bowl and cut butter into the mix with two forks or a pastry blender into pea-sized balls. Add milk and mix until just combined.

Transfer dough to a piece of greased parchment or plastic wrap and gently form into a disk. Place a second piece of greased wrap on top and gently pat or roll to 1½-inch thick. Use a biscuit cutter to divide into 9 pieces. Transfer to prepared baking sheet and bake 20 to 25 minutes until just starting to brown and the tops are splitting open. Cool on baking sheet 5 to 10 minutes.

To make gravy, melt butter in large skillet over medium heat. Add mushrooms and cook, stirring until liquid is released and mushrooms are softened, about 5 minutes. Add garlic and cook until fragrant, about 1 minute.

Sprinkle with the flour and stir to coat vegetables. Cook until flour smells toasty, about 1 minute.

While stirring, slowly pour in vegetable broth then milk. Stir in salt and pepper and bring to a simmer. Cook, stirring, until gravy is thick. Stir in thyme and season to taste with salt and pepper.

Serve gravy over warm biscuits.