How to Make It
Preheat oven to 300°F. Line a 13- x 9-inch baking pan with heavy-duty aluminum foil, allowing 2 inches of overhang on all sides. Lightly grease foil with cooking spray. Combine chocolate and butter in top of a double boiler over simmering water, and cook over medium, stirring occasionally, until melted and smooth, about 6 minutes. Cool chocolate mixture 5 minutes. Place egg white in bowl of a heavy-duty stand mixer fitted with the whisk attachment, and beat on medium speed until frothy, about 1 minute. Increase speed to medium-high, and gradually add 2 tablespoons sugar, beating until stiff peaks form, 2 to 3 minutes.
In a separate medium bowl, whisk together eggs and remaining 2 tablespoons sugar. Whisk vigorously until light, fluffy, tripled in volume, and mixture makes ribbons, 4 to 5 minutes. Fold in chocolate mixture until incorporated. Gently fold in egg white mixture just until combined. Pour batter into prepared pan; using an offset spatula, smooth into an even layer to completely cover bottom of pan. Bake in preheated oven until a wooden pick inserted in center comes out clean, about 15 minutes. Transfer pan to a wire rack, and let cool completely, about 45 minutes.
Line a 13- x 9-inch baking pan with parchment paper, allowing 2 inches of overhang on 2 long sides; set aside. Combine dark chocolate, milk chocolate, and butter in top of a double boiler over simmering water, and cook over medium, stirring occasionally, until melted and smooth, about 3 minutes. Remove from heat, and stir in cornflakes and salt until well combined. Spread mixture in a very thin layer (about 1/8 inch thick) to completely cover bottom of prepared pan. Freeze until set, at least 1 hour or up to 2 days. Using parchment paper as handles, lift chocolate crunch from pan in one piece. Carefully remove parchment, and place chocolate crunch sheet on top of cooled cake layer in baking pan. Freeze, uncovered, while preparing mousse.
Combine milk chocolate and dark chocolate in top of a double boiler over simmering water, and cook over medium, stirring occasionally, until melted and smooth, about 10 minutes. Let chocolate stand until slightly cool, about 15 minutes. Meanwhile, beat heavy cream and salt in bowl of a heavy-duty stand mixer fitted with the whisk attachment on medium speed until fluffy but still pourable (not quite soft peaks), about 3 minutes. Fold half of the whipped cream into slightly cooled chocolate until combined. Gently fold in remaining whipped cream. Spread mousse on top of frozen chocolate crunch layer in baking pan. Using an offset spatula, smooth mousse to sides of pan in an even layer to completely cover surface. If needed, dip offset spatula in hot water, and dry with a towel to make top layer of mousse as level as possible. Chill, uncovered, until set, about 2 hours.
Combine cherries and juice, pomegranate juice, and chile in a blender. Process until smooth, about 45 seconds. Pour mixture through a fine wire-mesh strainer into a bowl; discard solids. Sprinkle gelatin over 3 tablespoons cold water in a small bowl; let stand 5 minutes. Meanwhile, whisk together sugar and pectin in a small saucepan. Add cherry mixture and corn syrup to sugar mixture. Bring to a boil over medium-high, whisking often. Boil, whisking constantly, 2 minutes. Remove from heat, and whisk in bloomed gelatin until dissolved. Transfer mixture to a medium bowl, and let cool completely, about 2 hours. Pour glaze over chilled mousse layer. Tilt pan to evenly cover surface. Chill, uncovered, until glaze is set, about 1 hour. Prepared cake can be chilled up to 2 days.
When ready to serve, use foil handles to carefully lift cake from pan. Run a hot offset spatula along edges to break seal between cake and foil. Carefully remove cake from foil, and transfer to a cutting board. Using a hot, thin knife (not serrated) and dipping in hot water and drying knife between each cut, trim edges of cake to form an 11 1/2- x 8-inch rectangle. Cut rectangle in half lengthwise, and cut each half into 9 (about 4- x 1 1/4-inch) rectangles.