Instructions

1. To make the graham crust: Mix all of the ingredients together in a small bowl until the crumbs are moistened. Grease a 9-inch deep dish or a 10-inch pie plate and press 1 ¼ cups of the graham mixture into an even layer across the bottom and up the sides of the dish. Reserve the rest of the graham mixture and set the pie dish aside.
2. To make the brownie filling: Preheat oven to 350° F. Combine the bittersweet chocolate and butter in a small saucepan and stir until melted and smooth over medium-low heat. (Or heat the two in a bowl in the microwave at 30-second intervals until glossy and smooth.)
3. In the bowl of a stand mixer fitted with the whisk attachment, whip the eggs and sugar together on high speed for 3-4 minutes, until thickened, pale, and fluffy. Swap out the whisk for the paddle attachment and mix the chocolate into the eggs on low for a few seconds and then increase the speed to medium and beat for 1 minute - the mixture should be completely incorporated with no streaks. Scrape down the sides and bottom of the bowl with a rubber spatula.
4. Stir in the flour, cocoa powder, and salt on low speed for about 1 minute. If there are still clumps of flour remaining, continue stirring for another 30 seconds. With the mixer on low, pour in the heavy cream and stir for 30-45 seconds, until the mixture loosens up and the cream disappears. Scrape down the sides and bottom of the bowl again. Fold in the remaining ¼ cup of graham mixture into the brownie batter. Place the prepared pie dish on a sheet pan, transfer the brownie batter into the pie shell, and level off the top.
5. Bake for 25 minutes. The pie should puff slightly around the edges and form a sugary crust on top. If after 25 minutes, the center is still jiggly, bake for another 5 minutes. Lower the oven temperature to 300° F and wash out the mixer bowl if you will make the crumb topping next. Cool the pie completely on a wire rack. Either serve dusted with powdered sugar and ice cream, or continue on with the hot fudge sauce and crumb toppings.
6. To make the chocolate crumb topping: Combine the flour, cornstarch, sugar, cocoa powder, and salt in the bowl of a stand mixer fitted with the paddle attachment; blend on low until fully incorporated. Add the melted butter and stir until the mixture stars coming together in small clusters. Scatter the clusters in an even layer on a parchment- or silicone-lined baking sheet.
7. Bake for 20 minutes, breaking them up every 5-6 minutes. When finished, they should be slightly moist - they will dry and harden as they cool. Allow the crumbs to cool completely before using.
8. To make the hot fudge sauce: Combine the chocolate, cocoa powder, and salt in a medium bowl. Heat the corn syrup, sugar, and heavy cream in a small saucepan over high heat, stirring occasionally, until the mixture just comes to a boil. As soon as it boils, pour the hot mixture over the chocolate mixture and let it sit for 1 minute. Slowly whisk the hot liquid into the chocolate mixture and gently whisk until combined, glossy, and smooth, about 1-2 minutes. Allow the sauce to cool to room temperature before proceeding.
9. To assemble: Pour the fudge sauce over the top of the pie in an even layer, leaving a ½-inch boarder of brownie peeking out around the edges. Cover the fudge sauce with crumbs. Note: for both of these toppings, you can add less if you prefer. The fudge sauce will keep in the fridge for a few weeks; the crumbs, stored in an airtight container, will keep in the freezer for up to 1 month. I reserved about 1 cup of the crumbs for another use and stored them in the freezer.
10. Serve the pie right away or chill in the fridge for an hour or so.

Storage: Leftovers will keep, wrapped tightly, in the fridge for 3-4 days or in the freezer for up to 1 month.