In a small pan, sauté the onion and celery in butter over medium heat until tender. Remove from heat and set aside.
In a separate, larger skillet, cook the sausage and mushrooms until the sausage is no longer pink. Drain the sausage fat. Add the onion and celery (and the butter it was cooked in) and stir together.
In a large bowl, combine the breadcrumbs and seasonings with the sausage/vegetable mixture. Moisten with wine and broth. Add the egg and mix well. If the stuffing seems too dry, mix in more broth. You want it to be pretty moist- it will dry out more in the oven.
Use this stuffing to stuff your turkey, or place in a greased 9x13-inch casserole dish and bake (covered) at 375 degrees F. for 40 minutes- then remove cover and bake for an additional 10 minutes.
Notes
You can certainly use all chicken broth in place of the white wine.
Mom likes to slow-cook (simmer) the giblets and liver, and she chops some of that up and adds it to the stuffing too.