Sift 1.5 tbsp of cocoa powder into a microwave-safe mug. Set aside 1 cup of oat milk. Add 1.5 tbsp of plant milk to the mug and stir it into a smooth paste. Add the remaining milk and heat it for 20-30 seconds. Stir it until smooth, add the sugar, and heat for another 30 seconds. Heat it until hot, stirring in between. Add the vanilla and salt before enjoying. This makes one serving.