Place the cubed butternut squash, chopped apples, onion, and minced garlic into the slow cooker.
Pour the vegetable broth over the vegetables and add the cinnamon, nutmeg, salt, and black pepper.
Stir once to distribute the spices, then cover and cook on low for 6 to 7 hours until the squash is very soft.
Turn off the heat and use an immersion blender to puree the soup directly in the slow cooker until smooth.
Stir in the heavy cream until fully combined. Taste and adjust salt if needed before serving.