Cook the bacon in a skillet over medium heat until crisp. Remove the bacon to a paper towel and set aside, leaving the drippings in the pan if desired for extra flavor.
Add the diced potatoes, sliced leeks, diced onion, minced garlic, chicken broth, thyme, salt, and pepper to the slow cooker. Stir to combine.
Cover and cook on low for 6 to 7 hours, until the potatoes are very soft.
Use an immersion blender to puree the soup until smooth, or carefully transfer it to a blender in batches.
Stir in the heavy cream and let the soup warm for 10 more minutes on low.
Crumble the cooked bacon and sprinkle it over each bowl before serving.