Preheat oven to 350°.
Using a cast iron skillet, add butter to skillet and allow it melt on medium low heat.
Once butter has melted, add the fresh herbs of rosemary, thyme, and sage to the skillet and allow the herbs to cook for 15 minutes until they're fragrant.
Remove the herbs from the skillet and discard them.
Add the poultry seasoning, salt, and pepper to the skillet and cook for 1 minute.
Increase the heat to medium and add the chopped celery and leeks to the skillet and cook for 7 minutes until they are soft.
Add the chicken or turkey stock to the butter and vegetables and stir together.
Pour the mixture over the bread pieces in the large bowl and toss all ingredients together until the mixture has been soaked up by the bread.
Place the bread mixture back into the cast iron skillet and bake the stuffing for 20-25 minutes until it's golden brown.