Cook bacon in a large pot until crispy, set aside, and reserve about ¼ cup pan drippings. Add butter, melt, and sauté onions, carrots, celery, and garlic for 5 minutes. Sprinkle flour, whisk for 2-3 minutes.
Remove from heat, slowly whisk in chicken broth until smooth. Return to heat, add bouillon cube, thyme, bay leaf, salt, pepper, and potatoes. Bring to a boil, then simmer for 20 minutes until potatoes are tender.