In a small bowl, combine 2 tablespoons of half-and-half with the arrowroot, whisking until smooth.
Place remaining 1/2 cup of half-and-half in a small saucepan over medium heat. Bring to simmer. When the half-and-half begins to bubble around the edges, whisk in sugar. Whisk in the arrowroot mixture until the half-and-half thickens slightly (usually less than a minute).
Remove from heat and quickly whisk in the chocolate until smooth.
Pour into espresso cups, top each with whipped cream.