Whisk the cocoa powder, sugar, cornstarch, powdered milk, cinnamon, salt and vanilla powder together with the milk in a saucepan. Bring to a boil while continuing to stir the mixture so as to not to burn the chocolate.
Add the whipping cream to the bottom of your serving mug and tap the bottom to settle. Pour the hot chocolate mixture over the whipping cream in the serving mug. Keep watching the reaction of your Volcano Eruption.
Add chocolate shavings and pistachios on the top of your volcano.