1. Heat oven to 275 degrees. Tear bread into cubes and spread evenly on baking sheets. Bake until dried, about 40 minutes. Remove from the oven and cool.
2. Increase oven temperature to 375 degrees. Melt 1-2 tablespoons of butter in a Dutch oven or deep pot over medium heat.
3. Add onion, apples, and celery. Season with salt and pepper and stir. Cook 7-10 minutes, until translucent. Add olive oil if necessary to keep vegetables from burning.
4. Add sausage and break apart with a wooden spoon. Cook until crumbly and slightly browned.
5. Add garlic, herbs, and red pepper flakes, and cook for 2-3 minutes, until fragrant.
6. Remove pot from heat.
7. Whisk chicken stock and eggs in a separate bowl. Season with salt and pepper.
8. Slowly pour egg mixture into the pot while constantly stirring to avoid scrambling eggs.
9. Add bread to the pot and stir 2-3 minutes, until liquid is almost entirely absorbed.
10. Line muffin pan with paper liners. Scoop stuffing mix into muffin tins.
11. Bake for 30-45 minutes. Cover muffins with foil If they start to brown too quickly.
12. Remove muffins and let cool. Then remove muffins from the tin and serve warm.