You need a commercially available mug or, like me, an enamel mug. Please do not use a cup that is too small or divide the drink into two cups.
Divide the biscuits and separate the cream from the biscuits. Finely grind the biscuits in a freezer bag with a rolling pin or in a blender.
Beat the whipped cream almost until stiff, then add the oreo cream and mix everything together with a hand mixer.
Pour the cocoa or milk tea into the cup, cover with plenty of oreo whipped cream and then spread the oreo biscuit crumbs on top. Possibly decorate with something edible. There are no limits to the design options.