Start by gathering all your ingredients for the slow cooker blueberry butter. Rinse blueberries under cool water, then drain. Zest and juice one lemon.

In a spacious slow cooker, add the rinsed blueberries, lemon zest, lemon juice, light brown sugar, honey, ground cinnamon, and optional ground nutmeg. Stir gently.

Cover the slow cooker and cook on high for 1 hour. Watch for bubbling and steam indicating that it's cooking perfectly.

Once the hour is up, carefully remove the lid and transfer the mixture to a blender. Blend until smooth for a creamy consistency.

Return the blended mixture to the slow cooker, propping the lid with a wooden spoon to let excess liquid evaporate. Cook on low for 4-5 hours until thickened.

When thickened, ladle the warm blueberry butter into sterilized glass jars. Seal tightly while still warm for freshness.