In a medium bowl, mix graham cracker crumbs, melted butter, and sugar until well combined. Press firmly into the bottom of a 9-inch springform pan to form an even crust. Freeze for 15 minutes to set.

In a large mixing bowl, beat heavy cream until stiff peaks form. In another bowl, whisk together sweetened condensed milk, orange zest, cinnamon, nutmeg, and vanilla extract.

Gently fold the whipped cream into the sweetened condensed milk mixture until fully incorporated. Then, fold in the softened vanilla ice cream until smooth and creamy.

Pour the ice cream mixture over the prepared crust in the springform pan. Smooth the top with a spatula. Cover with plastic wrap and freeze for at least 6 hours, or preferably overnight.

Before serving, remove the cake from the freezer and let it sit at room temperature for 5–10 minutes to soften slightly. Top with whipped cream and candied orange peel if desired.

Slice and serve immediately. Store leftovers covered in the freezer for up to 2 weeks.