• Preheat your oven to 350°F. Grease 2 9-inch round baking pans and set them aside.

Prepare the chocolate cakes.

• In a large bowl, place the flour, xanthan gum, cocoa powder, salt, baking soda and sugar, and whisk to combine well.
• Create a well in the center of the dry ingredients and add the sour cream, oil, eggs, vanilla, and water, and mix to combine well. The batter should be very thickly pourable.
• Divide the batter evenly among the prepared pans, smooth into an even layer and place in the center of the preheated oven.
• Bake until a toothpick inserted in the center of the cakes comes out mostly clean or with a few moist crumbs attached (about 30 minutes), rotating the cakes in the oven halfway through baking. Do not overbake.
• Remove the cakes from the oven and allow to cool for 10 minutes in the pan before inverting onto a wire rack to cool completely.

Prepare the cookie crunch.

• In a medium-sized bowl, place the chocolate sandwich cookie crumbles.
• In a separate, small bowl, place the chopped chocolate and coconut oil and melt in the microwave in short, 30-second bursts until melted and smooth.
• Pour the melted chocolate and coconut oil mixture over the top of the cookie crumbles. Mix to combine, and set aside.

Prepare the optional frosting.

• In the bowl of a stand mixer fitted with the paddle attachment or a large bowl with a handheld mixer, whip the butter until light and fluffy (at least 4 minutes).
• Add the cocoa powder, confectioners’ sugar, salt, sour cream, and vanilla, and beat on medium speed until the powder is absorbed by the butter.
• Turn the mixer speed up to high and beat until very well-combined and light and fluffy but holds its shape. Set the frosting aside.

Prepare the pan for assembly

• If you’re using an acetate cake collar, cut a piece of acetate that a bit longer than the circumference of the springform pan.
• With the pan disassembled, position the acetate collar along the perimeter of the bottom of the pan, with the ends overlapping one another a bit.
• Place the rim of the pan in place, and close it around the acetate collar, avoiding any buckling of the collar.

Assemble & freeze the cake.

• Place the first cake on the bottom of the springform pan, right side up.
• Add about 2/3 of the chocolate crunch pieces into the prepared ice cream, and mix gently to combine. Scrape the ice cream onto the top of the bottom cake in the pan, and spread it into an even layer.
• Scatter the remaining 1/3 of the chocolate crunch evenly on top of the ice cream.
• Top with the second chocolate cake layer, positioned upside down, so the top of the cake is completely smooth and level. Press the top cake down firmly to help the layers adhere to one another.
• Transfer the prepared chocolate frosting to the top of the layer cake, and spread it into an even layer with a large spatula.
• Place the cake in the freezer to set for about 4 hours or until the ice cream is firm to the touch, but the cake can still be cut.

Serve.

• Release the sides of the springform pan and lift off the acetate collar. If the chocolate cake is fully frozen, allow the cake to sit at room temperature for about 30 minutes or until you can slice the cake.
• Using a large serrated knife, slice the cake in half, straight down the middle. Slice the halves of cake into wedges and serve.