In a 12-inch cast-iron skillet, cook bacon over medium heat until crisp. Remove bacon using a slotted spoon, and let drain on paper towels, reserving drippings in skillet.
Increase heat to medium-high. Add mushrooms; cook, stirring occasionally, until browned, 3 to 4 minutes. Remove from skillet. Add sausage; cook, stirring frequently, until browned and crumbly. Add shallot, onion, and celery; cook, stirring occasionally, until tender, about 10 minutes. Remove from heat.
In a large bowl, stir together sausage mixture, cornbread, broth, eggs, thyme, rosemary, pepper, salt, mushrooms, and half of bacon. Spoon into same skillet. Top with remaining bacon.
Bake until lightly browned, about 30 minutes. Garnish with thyme, if desired.
Recipe by Southern Cast Iron at https://southerncastiron.com/sausage-and-bacon-mushroom-dressing/