Cook bacon in a skillet over medium heat, stirring often, until crisp, about 5-7 minutes. Using a slotted spoon, transfer bacon to paper towels to drain. Reserve 1 tbsp of bacon grease and discard the rest of the grease.
In a slow cooker combine the 1 tbsp bacon grease, leeks, celery, garlic, cauliflower, broth, salt, and pepper. Cook on LOW for about 4 hours until vegetables are tender.
Remove about 1 cup of vegetables with a slotted spoon and finely chop.
Pour remaining mixture into a blender (or use a hand blender) and add half-and-half. Remove the center piece of the blender lid to allow steam to escape, attach lid, and place a clean towel over opening in lid. Process, starting slowly and increasing speed until very smooth, 1-2 minutes. Return to slow cooker with chopped vegetables. Keep warm until ready to serve.