For the whipped topping, use either a whisk, handheld frother, or immersion blender with a whisk attachment (the whipping time will be slightly longer using the first two methods).
Stir together the espresso powder, erythritol, and hot water in a pint-sized glass jar, or a tall, narrow glass.
Insert the immersion blender into the glass, and whisk for about 3 minutes on high speed. As the dark coffee mixture is whipped, it will double in volume and turn into a light brown whipped cream.
Fill a large glass with ice, about ⅔ full. Pour in the almond milk, vanilla extract, and combine.
Spoon the whipped coffee on top, and stir just before serving.