Start by chopping all your vegetables—sweet potatoes, carrots, celery, and butternut squash—into uniform, bite-sized pieces for even cooking.
In a skillet, heat olive oil over medium heat and add the minced garlic, cooking for about 30 seconds until fragrant and slightly golden.
Pour the cooked garlic and oil into the slow cooker, then add the chopped root vegetables, dried thyme, and vegetable broth. Stir to combine everything well.
Cover the slow cooker and cook on low for 6 hours, until the vegetables are tender and starting to caramelize at the edges, filling the kitchen with a warm aroma.
Once cooking is complete, open the lid and stir in the chopped kale. Let it wilt for about 5 minutes, adding salt and pepper to taste.
Serve the soup hot, with a sprinkle of fresh herbs or crusty bread if desired, enjoying the colorful, hearty mixture of tender vegetables and fragrant broth.