Frangipane, an almond-flavored filling, was named after the 16th-century Marquis Muzio Frangipani, who invented a bitter-almond scent for perfuming gloves. Parisian pastry chefs were so enthusiastic, they created their own edible version.
Place butter and sugar in the bowl of an electric mixer fitted with paddle attachment. Beat until light and fluffy. Add egg, ground almonds, rum, almond extract, and flour; beat until smooth. Store in an airtight container, refrigerated, up to 4 days.