Crush about 10 Oreo cookies into fine crumbs and set aside.
Line an 8 x 3-inch round cake pan with two pieces of plastic wrap, leaving enough overhang to easily lift the cake out later.
Let the 1.5-quart container chocolate ice cream sit at room temperature for about 20 minutes, or until softened.
Spread the softened chocolate ice cream evenly into the prepared cake pan. Freeze for 30 minutes.
Meanwhile, place 6 ounces semi-sweet chocolate chips, 3 tablespoons light corn syrup, and 1/2 teaspoon vanilla extract in a medium heatproof bowl.
Heat 1/2 cup heavy whipping cream until it just begins to simmer. Pour it over the chocolate chip mixture and let it sit for 2 to 3 minutes, then whisk until smooth.
Remove the cake from the freezer and spread the chocolate fudge evenly over the chocolate ice cream. Freeze for 10 minutes.
Sprinkle 3/4 cup Oreo crumbs evenly over the fudge layer. Return the cake to the freezer for about 2 hours, or until mostly firm.
Let the 1.5-quart container vanilla ice cream soften at room temperature for about 20 minutes. Spread it evenly over the Oreo layer and freeze for 2 to 3 hours, or until completely firm.
Lift the cake out of the pan using the plastic wrap and transfer it to a serving plate or cake board. Return it to the freezer while preparing the whipped cream.
In a large mixing bowl, beat 2 cups cold heavy whipping cream, 1 cup powdered sugar, and 2 teaspoons vanilla extract until stiff peaks form.
Frost the outside of the frozen cake with the whipped cream and decorate with sprinkles, if desired.
Freeze the cake until ready to serve. For the best texture, let it sit at room temperature for 5 to 10 minutes before slicing.
Notes
You can use a 9 inch pan but the cake will not be as tall.