Crushed graham crackers or grated chocolate for decorating
To make the graham crackers
In a medium bowl, whisk together both flours, the baking soda, and salt and set aside. in a small bowl, combine the milk and vanilla and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the brown sugar, butter, and vegetable oil on medium-low speed until slightly fluffy, about 2 minutes. Be careful not to overbeat. Scrape the sides of the bowl with a rubber spatula. Add the honey and mix until just incorporated and scrape the bowl again. The mixture may look a bit curdled at this point.
With the mixer running on medium-low speed, add half of the flour mixture. Scrape the sides of the bowl. Add the milk mixture, then the remaining flour mixture. Beat until the dough is still crumbly, and not yet a cohesive mass. Scrape the sides of the bowl with a rubber spatula to fully incorporate all the ingredients.
Form the dough into two 2 1/2-by-5-inch blocks. Or, line an 8-by-4 in/20-by-10 cm loaf pan, preferably with straight sides, with plastic wrap and press the dough into the pan (forming one large block). Wrap the blocks (or pan) in plastic wrap, and freeze for 2 hours or overnight. If you choose to press your dough into a loaf pan to shape it, your crackers will be slightly smaller than the traditional cracker size.
Line two baking sheets with parchment paper.
Once frozen and super firm, unwrap the dough and cut off thin rectangular slices (1/8 to 1/4 inch thick). Do not be concerned if your rectangles are imperfect. Using the tines of a fork, prick the rectangles lengthwise in two rows.
Arrange the slices about 1 inch apart on a lined baking sheet and freeze them for at least 10 minutes. If you need additional baking sheets to fit all of your crackers, simply arrange them on additional sheets of parchment paper, and layer the cracker-covered papers one on top of the other on a baking sheet in the freezer. If you want to bake the crackers at some point in the future, wrap the trays in plastic wrap and freeze the slices for up to 1 week.
Position a rack in the center of the oven and preheat to 350 degrees.
Bake the frozen crackers until they are golden brown and relatively firm and dry, 13 to 15 minutes, rotating the sheets halfway through the baking time. Using a stiff metal or plastic spatula, immediately press down lightly on each cracker to flatten it. Let the crackers cool on the baking sheet for 2 to 3 minutes, then transfer them to a wire rack to cool completely. The crackers should be very crispy when cooled. If they are not, place them back in the 350 degree oven for 1 to 2 minutes more. Repeat with the remaining frozen crackers.
Store the crackers in an airtight container as soon as they have cooled. they will remain crispy at room temperature, tightly sealed, for about 24 hours. Freezing the baked crackers in a resealable plastic bag also works well, for up to 2 weeks. There is no need to defrost the crackers before assembling your cake.
To make the whipped cream
In the bowl of a stand mixer fitted with the whisk attachment, whisk together the egg whites, cream of tartar, and salt on medium speed until quite frothy. Add 1 Tbsp of the granulated sugar and whisk until soft peaks form. The peaks should flop over when the whisk is lifted. Be careful not to overbeat.
Meanwhile, in a small saucepan over medium heat, combine the remaining 3/4 cup granulated sugar, the corn syrup, and water. Using a wooden spoon or heatproof spatula, gently stir the mixture until the sugar dissolves completely. Attach a candy thermometer to the side of the pan. Increase the heat to medium-high and boil the mixture until it reaches the firm-ball stage, 246 to 248 degrees.
With the stand mixer on low, slowly add the sugar syrup to the beaten egg whites, aiming it away from the whisk. Increase the mixer speed to high and beat until the mixture reaches room temperature (you can test this by placing your hand on the bottom of the mixing bowl) and is quite shiny and airy, 5 to 7 minutes. Add the vanilla and whisk 1 minute more. Transfer to a large bowl and set aside.
Clean the bowl and whisk from the stand mixer and refrigerate them until quite cold, about 15 minutes.
Once chilled, remove the bowl and whisk from the refrigerator, add the cream, and whip it on medium speed until just thickened.
Increase the speed to medium-high and whip the cream until it holds stiff peaks that stand upright when the whisk is raised (the stiffer the cream, the more support it will provide the crackers in your cake).
Gently fold the whipped cream into the marshmallow cream, being mindful not to deflate the cream; it’s okay to leave fluffy morsels of marshmallow throughout. Set aside.
To make the pudding
In a medium saucepan, combine the granulated sugar, cocoa powder, cornstarch, and salt. Add the milk and cream and whisk. add the egg, whisk again, and place the saucepan over medium-high heat, whisking constantly.
Once the mixture begins to thicken and bubbles begin popping on the surface, decrease the heat to medium and whisk vigorously for 45 seconds. Remove the pan from the heat.
Add the butter and vanilla and whisk until they are incorporated. If the pudding has any lumps, strain it through a medium-mesh wire sieve into a heatproof bowl.
The pudding should be used almost immediately; it should still be warm and relatively pourable when you layer it with the crackers.
To assemble your cake
Lightly coat the sides of a 9x3-inch springform pan with cooking spray and line the sides with a strip of parchment paper. Using a small offset spatula or the back of a spoon, spread a generous layer of pudding on the bottom of the pan.
Cover as much of the pudding as possible with a layer of graham crackers, filling any gaps with broken crackers (breaking them yourself, if necessary). The pieces should touch. The goal is a solid layer of graham crackers.
Generously spread some of the whipped cream over the crackers, add another layer of crackers and continue layering in this order (pudding, graham crackers, whipped cream, graham crackers) until you run out or reach the top of the pan.
Spread the top of the cake with a final layer of whipped cream and gently cover it with plastic wrap. Refrigerate the cake for 24 hours.
Remove the cake from the refrigerator prior to serving and peel off the plastic wrap. Run a paring knife between the paper and the pan. Open the clamp, remove the pan sides, and gently peel back the paper. Transfer the cake, still on the pan bottom, to a serving platter and sprinkle crushed graham crackers or grated chocolate on top. Using a knife, slice it into wedges and serve.
When slicing the graham crackers, do not fret if the slices are a bit crumbly. Just use your fingers to smoosh the crumbly bits back into the slice/dough.