Add the sweetened condensed milk, vanilla extract, and salt to a large mixing bowl. Whisk until well combined and set aside.

In the bowl of a stand mixer fitted with the whisk attachment, or in a large mixing bowl using a handheld mixer, add the heavy whipping cream. Start mixing on low speed. Once the mixture starts to increase in volume, increase the speed to medium-high and continue mixing until stiff peaks form.

Gently fold half of the whipped cream into the sweetened condensed milk mixture, then fold in the remaining whipped cream until just combined.

Scoop the ice cream mixture into the prepared springform pan and smooth it out into one even layer.

Place a piece of plastic wrap directly onto the surface of the ice cream and transfer it to the freezer to freeze overnight (or for at least 8 hours).

In a large mixing bowl, sift the flour, cocoa powder, baking powder, baking soda, and salt together. Whisk in the granulated sugar and brown sugar until well combined. Then, add the oil, buttermilk, eggs, and vanilla extract and mix until just combined. The batter will be thick like brownie batter at this point.

Add the instant espresso powder to the cup of boiling water and mix until fully dissolved. Add to the mixing bowl and mix until everything is just combined. The batter will be thin.

Evenly distribute the batter between the two prepared cake pans.

Bake for 28 to 30 minutes or until a toothpick inserted into the center of the cakes comes out clean and the tops spring back when lightly touched.

Remove from the oven and transfer to a wire rack to cool completely. Once cooled, wrap the cake layers tightly with plastic wrap and refrigerate until ready to use.

Start mixing on low speed. Once the mixture starts to increase in volume, increase the speed to medium-high and continue mixing until stiff peaks form.

Remove the ice cream from the freezer. Peel the plastic wrap off the top of it and lift it out of the pan using the overhang from the plastic wrap.

Place it upside down on top of the cake layer and peel off the plastic wrap. Place the second cake layer upside down on top of the ice cream layer. If the ice cream is overhanging the cake layers a little bit, use an offset spatula to help smooth it out evenly with the cake layers.

Working quickly, spread a thin layer of whipped cream over the outside of the cake to catch any crumbs. Then, use the remaining whipped cream to frost the top and sides of the cake. If you want to pipe some decorations on top, I recommend reserving 1 to 1 ½ cups of whipped cream. If using sprinkles or other toppings, add them to the cake at this point.

Once the cake is decorated, place it in the freezer for 30 minutes to 1 hour before slicing and serving. If you leave the ice cream cake in the freezer for several hours before serving, let it sit at room temperature for a few minutes so that it’s easier to slice.