1Preheat the oven to 350°. Parchment line (cut 8" circles) and spray two cake pans with nonstick cooking spray. In a medium bowl, whisk the flour with the baking powder, baking soda and salt. In a small bowl, whisk the cocoa powder with the water until a smooth paste forms. In the bowl of a stand mixer fitted with the paddle, beat the butter with the brown sugar at moderate speed for 3 minutes. Beat in the egg, egg yolk, buttermilk and vanilla. At low speed, beat in the dry ingredients and cocoa paste in 2 alternating batches.
2Scrape the batter into the prepared pans and bake for 30 to 35 minutes, until a toothpick inserted in the center comes out with a few moist crumbs attached. Let the cake cool until you can handle the pan in your hands, and remove from cake pan. Let the cake cool completely on a rack. Leave the oven on.
1Using a serrated knife, cut off the top of the cakes so they are even. Use the fine crumbles leftover (crumble with your hands) and spread on a baking sheet. Bake for 10 to 12 minutes, turning the pan halfway through, until the crumbs are crisp. Let the crunchies cool completely.
1Saucepan: Over medium high heat, combine cream, sugar, and syrup until dissolved (3 min). Add the chocolate and salt and bring to a boil and whisk vigorously. Lower to a gentle simmer so that the bubbles percolate in the center in the pot. Cook, stirring often to avoid scorching the bottom. You are cooking for about 20-30 minutes until the mixture breaks and the oils separate from the solids. Now, whisk in the butter. Let cool. Last up to 6 months in refrigerator.
1Using scissors, trim a sheet of clear acetate to 6-by-24 inches. Wrap the acetate around the cake and secure it with tape.
1First Layer: Cake. Scoop & spread ice cream with offset spatula. Spread & pour on fudge. Sprinkle crunchies. Freeze firm.
2Second Layer: Cake. Scoop & spread ice cream with offset spatula. Spread & pour on fudge. Sprinkle crunchies. Freeze firm.
Whipping Cream Layer
1In the bowl of a stand mixer fitted with the whisk, beat 1 1/2 cups of the heavy cream with the granulated sugar until it holds soft peaks. Spread the whipped cream over the last layer. Freeze the cake overnight.
Chocolate Ganache Topping
1Place the chocolate in a heatproof medium bowl. In a small saucepan, bring the remaining 1 cup of heavy cream to a boil.
2Pour the hot cream over the chocolate and let stand until melted, about 5 minutes. Stir until smooth, then tap the bowl on the counter to pop any air bubbles. Let the ganache cool slightly (but still pourable).
3Carefully peel the acetate off the cake. Transfer the cake to a rack set over a rimmed baking sheet. Working quickly, pour the ganache onto the center of the cake in one fluid motion, allowing the excess to drip over the side. Freeze the cake until the ganache is firm, about 30 minutes.
4Freeze the cake for 30 minutes before serving.
Credit: Food & Wine DIY Ice Cream Cake Recipe, Modified
Need overnight freezing before serving.