Add the seafood shells, onions, carrots, and celery and saute for 10 minutes, or until lightly browned. Add the garlic and cook 1 more minute.
Add 1 1/2 quarts of water, wine, tomato paste, salt, pepper, and thyme. Bring to a boil, then reduce the heat and simmer for 30 minutes.
Strain stock through a sieve, pressing the solids.You should have approximately 1 quart of stock. You can make up the difference with water or wine if you need to.
To Make the Chowder
Add olive oil to a 3 quart or larger soup pot over medium heat. When oil begins to shimmer, stir in carrot, onion, and celery, and saute until onion is translucent, about 3 minutes. Add garlic and saute for another minute, stirring constantly so that garlic doesn't burn.
Sprinkle flour over the vegetables and stir to combine. They will appear pasty. Turn heat up to medium high and slowly whisk in seafood stock, about 1/4 cup at a time, until all stock has been incorporated.
Turn heat to high and bring to a light boil. Add potatoes and all seasonings and reduce heat slightly. Cook 8 minutes, stirring occasionally, until potatoes are fork tender.
In the final 3 minutes of cooking time, stir in cooked seafood and half and half or milk. Taste and add additional seasonings as desired.