The Sugar Free Coquito is something we stumbled upon when investigating milk substitutes. Why replace milk? Carbs. They don’t have much, but they do exist. We usually use heavy cream in lieu of actual milk, but that can add a viscosity that can be a little overwhelming if more than an ounce is called for.
Also, there are cocktails that call for 4 ounces of milk, which obviously rules out using the heavy cream.