Prepare the Brownie Layer:
Preheat your oven to 350°F (176°C). Line a 9-inch round cake pan with foil, leaving enough overhang around the edges for easy removal later.
In a large bowl, combine the canola oil, sugar, eggs, and vanilla extract. Add the all-purpose flour, cocoa powder, and salt, mixing just until combined. Be careful not to overmix. Pour the batter into the prepared pan and bake for 30-35 minutes, or until the edges are set and a toothpick inserted comes out with moist crumbs (not wet batter). Allow the brownie to cool completely in the pan.
Prepare the Ice Cream Layer:
Allow the ice cream to soften slightly for easier handling. Line another 9-inch round cake pan with plastic wrap, ensuring there is enough overhang to cover the ice cream layer.
Spoon the softened ice cream into the prepared pan, smoothing it into an even layer. Press out any air pockets, then cover with the overhanging plastic wrap. Freeze for at least 8 hours, or up to 3 days.
Assemble the Cake:
Once the brownie layer has cooled completely, remove it from the pan and discard the foil. Place the brownie on your desired cake stand or serving plate. Spread the hot fudge sauce evenly over the top of the brownie.
Remove the ice cream layer from the pan and peel away the plastic wrap. Quickly place the ice cream layer on top of the brownie and hot fudge layer. Cover the entire cake with plastic wrap and freeze for 30 minutes to allow it to set.
Prepare the Whipped Cream Frosting:
In the bowl of a stand mixer, whip the heavy whipping cream, powdered sugar, and vanilla extract together until stiff peaks form.
Remove the cake from the freezer and spread the whipped cream frosting evenly over the entire cake, including the sides. If desired, pipe decorative designs with the whipped cream. Return the cake to the freezer for another 30 minutes or until the whipped cream is solid.
Serve and Enjoy:
Before serving, you can add sprinkles on top for extra decoration. Slice and enjoy this decadent Brownie Ice Cream Cake!