Using a culinary torch toast mini vanilla marshmallows. Alternatively use a gas hob or a candle. Either way be careful not to burn yourself.
For the chocolate sauce in a small saucepan combine 80ml water, the unsweetened cocoa powder and 45gr sugar, cook on medium 2-3min until smooth. Take off heat, add the dark chocolate, leave to fully dissolve, then return to medium heat, stir until smooth and take off heat.
Dissolve the cornstarch in 50ml whole milk, leave to rest.
For the ice cream base in an another small saucepan combine the heavy cream, the leftover milk, 70gr sugar, pinch salt, stir, place on medium heat, bring to an almost boil, add the cornstarch milk and cook stirring constantly until thickened. Take off heat, add the cream cheese and the chocolate sauce, mix until smooth and combined. Cool to room temperature, then transfer to the fridge overnight.
Freeze in your ice cream maker according to the manufacturer's instructions adding the torched marshmallows at the last couple of minutes of churning. Store in an airtight container or spoon right away.