Combine the mini chocolate chips and mashmallows with the milk in a small saucepan. Heat over medium heat, stirring occasionally, until the mashmallows and chocolate chips melt. If you want extra body in the drink, use a handheld mixer or milk frother before combining it with the espresso.
Using the Aeropress or your espresso machine, pull a shot of espresso and pour it into your mug of choice. Pour in the heated, frothed, and flavored milk. Stir to combine. If desired, top with whipped cream and extra chocolate chips and marshmallows. Enjoy!