To start, line three 3 inch diameter and 1.75 inch tall ring molds with acetate and place on a silpat lined baking sheet. Set aside.
For the cake, preheat the oven to 325 F. Line a half sheet pan with a silpat or spray lightly with nonstick spray, line with parchment paper, and spray the parchment.
Sift the flour, cocoa powder, baking soda, and baking powder into a medium bowl. Add the salt and stir to combine.
Place the eggs, sugar, and vanilla paste in the bowl of a stand mixer fitted with the whisk attachment and mix on medium-low speed for about 1 minute to combine. Increase the speed to medium and whip for 5 minutes, until the mixture is thick and pale yellow. Scrape down the sides and bottom of the bowl, then whip on medium-high speed for another 5 minutes, or until the mixture has thickened. When the whisk is lifted, the mixture should form a slowly dissolving ribbon.
Add the mayonnaise and whip to combine. Remove the bowl from the mixer stand and fold in the dry ingredients and water in 2 additions each.
Pour the batter into the prepared pan and, using an offset spatula, spread it in an even layer, making sure that it reaches into the corners. Bake for 10 minutes, until a skewer inserted into the centre comes out sean and the cake springs back when lightly touched. Set on a cooling rack and cool completely.
Lay a piece of parchment on the back of a sheet pan. Run a knife around the edges of the cake to loosen it and invert it onto the parchment. Remove the silpat or parchment from the top of the cake. Place in the freezer for at least 30 minutes.
Cut out three 3-inch diameter rounds from the cake while it is still frozen and place in the ring molds. Wrap the remainder of the cake in plastic wrap and freeze for up to 2 weeks (this is extra).
For the streusel, preheat the oven to 325 F. Line a baking sheet with parchment paper.
Combine the almond flour, graham crumbs, sugar, vanilla powder, and flour in a small bowl. Whisk to combine. Add the butter and quickly break it up with your fingertips until the mixture resembles coarse meal. Spread the streusel on the baking sheet in an even layer and freeze for 10 minutes.
Bake for 12 to 15 minutes, stirring the streusel every 4 minutes. Remove from the oven and cool completely. Spoon 40 g of streusel into each ring hold and gently press into the holds Store the remainder in an airtight container at room temperature for up to 4 days or freeze for up to 2 weeks.
For the custard, combine the milk and cream in a medium saucepan set of medium-high heat. In a small bowl, whisk together the egg yolks, sugar, and cocoa powder until slightly paler in colour.
When the milk mixture has come to a boil, slowly pour a small amount into the yolk mixture, whisking continuously. Continue tempering the yolks with the milk mixture, then transfer all of back into the saucepan. Cook over medium-low heat, stirring continuously with a rubber spatula, until the mixture has thickened enough to coat the back of a spoon and a thermometer reads 82 C.
Remove from heat and strain through a fine-mesh sieve into a bowl set over an ice bath. While the mixture is still warm, add the melted chocolate and emulsify with an immersion blender. Place a piece of plastic wrap directly on the surface of the custard and refrigerate for at least 3 hours, or overnight.
Fill a piping bag with the chocolate custard and pipe into the molds until it reaches the top of the molds. Smooth the top with an offset spatula and freeze for 4 hours, or overnight.
Remove the rings from the cakes, but keep the acetate on. Add a second layer of acetate 0.5 inches higher than the original acetate over top the original acetate. Place the rings back on.
For the meringue, combine the egg whites and sugar in the bowl of a stand mixer set over a saucepan of barely simmering water. Whisking constantly, bring the mixture to 60 C, then transfer to the stand mixer and whip on high speed until stiff peaks form, about 8 minutes. Add the vanilla paste and whip for 1 minute to combine.
Pipe the meringue into the rings until it reaches the top of the second layer of acetate. Smooth the top with an offset spatula and freeze for 30 minutes.
Place into the fridge 4 hours before serving but remove the rings and both layers of acetate while frozen. When ready to serve, use a handheld torch to toast the meringue while being careful not to scorch the custard.
Recipe and Photography by Hint Of Vanilla.