Stir together condensed milk, 1 cup Nutella, and vanilla extract until completely combined.
In separate bowl (preferably a chilled metal bowl), whip cream with electric mixer on high until stiff peaks form.
Add Nutella mixture to whipped cream, stirring briefly and then folding in until completely combined.
Pour into breadpan and swirl with remaining Tbsp Nutella.
Cover with clear wrap (or pour into other resealable container) and freeze at least 6 hours before serving.