Blend raspberries and sugar until smooth, then strain through a fine-mesh sieve to remove seeds. Set aside.

Whip heavy cream on medium-high speed until stiff peaks form, about 3 to 4 minutes.

Pour sweetened condensed milk and vanilla over the whipped cream and gently fold until no streaks remain.

Spoon the cream mixture into a loaf pan, add dollops of raspberry puree, and swirl with a knife. Smooth the top, cover, and freeze at least 6 hours. Let soften 5 minutes, then scoop and serve with fresh raspberries.