Crush nutmeg. Combine all the ingredients except oranges in a large bowl. Bring it to a boil and let it simmer on low heat under the lid for about 20 min.
Add sliced oranges, simmer for an additional 20 min. Remove from the heat, let it steep for another 20 min. Let it cool a bit and then strain.
Serve warm; garnish each glass with an orange slice and cinnamon stick.
Store in an air-tight jar or a bottle in the fridge for up to a week.