Slice the sourdough bread into thick slices and then each slice into ½ to 1-inch cubes. If you prefer a more rustic look, tear the bread into bite-sized pieces instead of cubing with a knife.
Either leave the spread out bread on a large baking tray overnight to dry out or, if you're short on time, toast in the oven preheated to 300 degrees Fahrneheit for about 30 minutes or longer, tossing and turning from time to time until the bread pieces are dried out. Cool and set aside.
Preheat (or increase temperature) the oven to 375 degrees Fahrenheit.
Melt 1 stick (8 tablespoons) butter over low-medium heat, add chopped onions and celery and sauté, stirring often until softened but not browned, about 10-12 minutes.
Add minced garlic and cook for one minute until fragrant.
If using white wine, add it now and cook to reduce, about 4 minutes. Turn the heat off.
Whisk together chicken or turkey broth and eggs until combined.
Chop up all the herbs you're using (parsley, thyme, sage).
Transfer the dried out bread pieces into a large bowl. Add sautéed onions and celery. Make sure to scrape all the bits and butter from the pan - that's where the flavor is!
Season with salt and pepper. Add chopped herbs.
Pour in ¾ of the broth-egg mixture and stir it together until the bread absorbs all the liquid. If the mixture seems not wet enough, add the remaining ¼ of the liquid. I like my stuffing crispy on the outside and custardy and fluffy inside so I use all 2 ½ cups of broth.
Grease a 9 x 13 casserole dish with butter or spray lightly with non-stick spray.
Transfer the mixture to the prepared dish and dot with 2 tablespoons butter cubed small.
Bake uncovered for 40-45 minutes until the edges are crispy and golden brown. If the top is not browned enough, increase the temperature to 410 degrees and bake or broil for a few more minutes. Watch the stuffing so it doesn't get too dark or burn.