Melt 1 tablespoon butter in a large skillet over medium-high heat, and brown sausage and mushrooms, breaking up sausage, about 6-8 minutes. Remove sausage and mushrooms with a slotted spoon and set aside, leaving the drippings in the skillet. (you should have about 2 tablespoons of drippings in the skillet, discard any more than that. If you haven't got enough, supplement with a little added butter).
Reduce heat to medium-low. Add onion and saute for 1-2 minutes, until translucent. Sprinkle over flour and whisk constantly until mixture begins to turn golden brown.
Combine half and half with milk and worcestershire sauce. Gradually whisk milk mixture into skillet; when the mixture has thickened and is just starting to bubble, return the sausage and mushrooms to skillet. Add garlic and season to taste with salt and pepper (adjust to suit your own taste, but remember you'll be adding the swiss cheese shortly). Reduce heat and simmer, covered, for about 15 minutes. Remove from heat and whisk in swiss cheese, until cheese has melted into sauce. (if your gravy is too thick, thin by whisking in a little more half and half or milk).
Meanwhile, bake refrigerated biscuits according to instructions.
To serve: Place 2 biscuits per person on a plate. Smother with rich sausage gravy. Sprinkle generously with parsley. Dig in!
Enjoy with family!