Peel and chop the sweet potatoes into 1-inch chunks, making sure they are uniform for even cooking. Place them into the slow cooker.
Roughly chop the onion and add it to the slow cooker along with the minced garlic. These aromatics will soften and infuse the soup with warmth and sweetness as they cook.
Pour in the vegetable broth, covering the sweet potatoes and aromatics. Secure the lid and set the slow cooker to low. Let it cook for 6 to 8 hours until the sweet potatoes are fork-tender and fragrant.
Once cooked, open the lid and check that the sweet potatoes are very soft and easy to mash. Use a fork to test their tenderness.
Using an immersion blender directly in the slow cooker or carefully transferring the mixture to a blender, puree the soup until it becomes silky smooth. This should take about 2-3 minutes, and the aroma will deepen as it turns velvety.
Taste the soup and season with salt, pepper, smoked paprika, and a pinch of cinnamon. If desired, add a squeeze of lemon juice or vinegar to brighten the flavors. Blend briefly to incorporate.
If the soup feels too thick, stir in a little hot broth or water until it reaches your preferred consistency. The final soup should be creamy, smooth, and inviting.
Serve the soup hot, garnished with your favorite toppings like a dollop of yogurt, chopped herbs, or toasted seeds if desired.
