The best soup in Brooklyn is from the Soup Bowl of Park Slope on 319 7th Avenue.
The Soup Bowl of Park Slope is seasonal restaurant/pop up shop that makes homemade soups fresh every single day during the cold months. That don't serve the same soups every moth but here are a few suggestions:
The lobster bisque. People drive from Manhattan to Brooklyn for this lobster bisque. This bisque is for foodies. This is not a casual bisque encounter. This is a bisque that was created by God, sent to you, and sanctioned by the international soup makers of the world. This is the mother load of all lobster bisques. You will never lose with this bisuq on your lips.
The chowders. Try any of the chowders. I've had the clam chowder, the New England chowder, and the chorizo vegetable chowder. They make amazing chowders with healthy amounts of meat and veggies.
Anything with bacon. I just started dabbling in pork in my adult life and I'm not a huge fan of it. I've never had a soup from this place that had bacon in it and it didn't taste amazing.