In a large skillet over medium-high heat, cook the bacon until crispy. Reserve half of the bacon for topping and place it in the refrigerator until you're ready to serve the chowder.
Add the potatoes, remaining bacon, 1 tablespoon bacon grease, onion, celery, carrots, garlic, and baby clams to the slow cooker.
Pour in the crushed tomatoes, chicken broth, tomato paste, clam juice, salt, pepper, dried parsley, dried thyme, and cayenne pepper. Give everything a good stir to combine.
Cover and cook on low for 6–8 hours or high for 3–4 hours, until the potatoes are fork tender.
Before serving, garnish each bowl with chopped parsley and the reserved crispy bacon.