Thaw spinach in the refrigerator overnight. To speed up the process, you can place in a bowl of cold water. Squeeze as much water out of the spinach as you can, then chop spinach on a cutting board. Set aside.
In a large mixing bowl, combine the sour cream, mayonnaise and dry soup mix. Stir in spinach, water chestnuts and green onions. Cover and refrigerate at least 1 hour or up to 24 hours.
To serve, cut the top off of the loaf of bread and pull out the insides, leaving about a 1-inch thick border all the way around and on the bottom of the loaf. (Save the bread for dipping). Pour the dip into the bread bowl and top with a few thinly sliced green onions or chives and some fresh cracked black pepper, if desired.
Serve with chunks of bread, potato chips, or veggies like sticks of bell peppers, carrots, cucumber and celery, or broccoli and cauliflower.
Make Ahead: Make the dip up to 24 hours in advance. Just give it a quick stir before serving.
Storage: Keep dip in an airtight container in the fridge. It will keep for 3-4 days. Freezing is not recommend as it will change the texture of the dip as it thaws.
How to serve: My favorite way to eat this dip is with chunks of bread for dipping. You can also use chips, crackers or veggies.
Using fresh spinach: 10 ounces of frozen spinach is equal to about 1 pound of fresh. Cook the spinach according to package directions, and cool completely. Squeeze dry in a clean kitchen towel.