In a large baking dish, toss together bread cubes, celery, and onions.
Add stock to the bread mixture and gently squeeze the mixture together with your hands to wet all of the bread.
Place the softened butter in small pats on top of the wet bread mixture and gently work in with your hands.
Add poultry seasoning, sage, salt, and pepper and work into the mixture until incorporated. Taste to test seasoning, and adjust if necessary.
Add beaten eggs and mix in until incorporated.
Transfer stuffing mixture to a buttered slow cooker.
Cook on HIGH for 30-45 minutes. Then switch to LOW and cook for an additional 3-4 hours.
Serve when done, or switch slow cooker to warm until ready to serve.
Customize your stuffing! We almost always add finely chopped gizzards to our stuffing, added at the same time as the eggs. You can add different meats, cheeses, and herbs to make it your own. Check out these yummy stuffing variations.
Do NOT lift the lid while cooking, as tempting as it may be! It will make it take longer to cook as the heat will escape, and it doesn't need stirring anyway!
A large (6 quart or more!) slow cooker is best with this amount of stuffing. Consider opting for a programmable Crock Pot like this one since holidays get chaotic. Then you won't have to think about it, and it won't be overcooked.
Bread needs to be damp but not soaking. See my video for my grandma's "squeezing out" technique.
Keep slow cooker on warm until ready to serve.
Make Ahead: Prepare the stuffing from steps 1-5 up to 24 hours before. Then cover and refrigerate until ready to cook. Don't transfer to the slow cooker until ready to cook (a cold slow cooker will increase the cook time by a lot). Increase cooking on HIGH to about 1 hour, then reduce to low and continue with the recipe.
If you'd like to try my grandma's original stuffing recipe, find it here.