In the bowl of a stand mixer, beat chilled heavy cream until stiff peaks have formed. With mixer on low speed, slowly stream in sweetened condensed milk followed by vanilla extract and pinch of salt. Stir in Fruity Pebbles.
Transer mixture to springform pan and freeze until firm, about two hours. Remove from freezer and top with frosting and additional sprinkles. Return to freezer and freeze until completely set, 4 hours or overnight.
To serve, remove sides of springform pan. Then, place a clean cutting board on top of cake and gently turn over using the cutting board as support. Quickly remove the plastic wrap and turn cake back over onto a serving plate.