Preheat oven to 375 degrees Fahrenheit; grease a 9x13 baking dish.

Melt butter in a large skillet over medium heat; cook mushrooms until they release moisture and brown.

Stir in sage, salt, pepper, and flour; cook one minute.

Slowly whisk in milk; simmer until gravy thickens.

Quarter biscuits; place in dish and top with gravy.

Bake 30 to 35 minutes.