Heat milk in medium saucepan over medium-high heat until it reaches the scalding point (edges of milk will begin to bubble, but milk will not boil). Meanwhile, in medium bowl, using whisk, beat together sugar and egg yolks until thick and pale yellow. Gradually whisk hot milk mixture into egg yolk mixture until incorporated; return to saucepan. Cook, stirring occasionally, until milk mixture thickens (it should reach 170°F on quick-read thermometer). Do not allow milk mixture to boil. Transfer hot custard to bowl; mix in thawed lúcuma pulp. Chill until cold.
In medium bowl, using hand blender or whisk, beat heavy cream until it thickens and forms stiff peaks (the cream will hold its shape and cling to the edges of whisk when raised). Mix 1/3 whipped cream mixture into chilled lúcuma custard until combined. Gently fold in remaining whipped cream. Transfer lúcuma-cream mixture to 1½-qt.bowl or loaf pan; cover with plastic wrap. Freeze until firm, about 3 hours, or up to 1 week.
To serve, scoop lúcuma ice cream into serving bowl; top with dulce de leche, if desired.