Prepare an ice bath by filling a medium metal bowl with ice and water.
Place the cream in a small saucepan and bring to a simmer over medium heat. Remove from the heat.
In a small bowl, beat the egg yolk and sugar until pale and thick, about 1 minute. Slowly drizzle in the hot cream, whisking constantly. Return the mixture to the pan and, stirring constantly, cook over medium heat until the sauce thickens and coats the back of a spoon.
Remove from the heat and add the Amaretto. Strain through a fine mesh sieve into a clean bowl and place in an ice bath, stirring until cool.
Cover with plastic wrap, pressing down against the surface to prevent a skin from forming, and refrigerate until well chilled, about 2 hours. Serve cold.
Yield: 1 cup