Fill the lower chamber of the moka pot with boiling water to just below the valve, then fill the funnel with ground coffee, tap the side to remove air pockets, and level the top with a knife. Do not tamp the grounds.
Screw on the upper chamber and place the moka pot over low heat. (If you're using a gas stove, keep the flame smaller than the base of the moka pot.) After a few minutes, you'll hear the water begin to boil, and the espresso will start to come out of the top.
While the water is heating, measure the sugar for the espumita into the creamer or a glass measuring cup. As soon as the first drops of espresso come out of the top of the moka pot, pour enough into the sugar to moisten it, then put the pot back on the heat. Whip the mixture with a spoon or an electric mixer until the espumita is light brown, thickened, and trebled in volume.
Once the stream of espresso in the moka pot is honey colored, remove it from the heat and immediately pour the espresso into the creamer with the espumita. Stir to combine.
Let the mixture stand until the espumita has floated to the top, then pour into tacitas (demitasse cups) and serve immediately.