Crust:

• 255g (1 ½ cups) graham crumbs
• 50g (¼ cup) granulated sugar
• 6 tbsp unsalted butter, melted

Brownies:

• 260g (9 oz) semi-sweet chocolate
• 113g (1 stick) unsalted butter
• 3 large eggs, room temperature
• 3 large egg yolks, room temperature
• 200g (1 cup) granulated sugar
• 100g (½ cup packed) dark brown sugar
• ¾ tsp salt
• 2 tsp pure vanilla extract
• 50g (½ cup) Dutch-processed cocoa powder
• 70g (½ cup) all-purpose flour
• 16 marshmallows
• 2 graham cracker wafers

1. Place the oven rack in the middle of the oven.
2. Preheat the oven to 350°F.
3. Butter a 9 x 9 inch baking pan and line with parchment paper.  Make sure to leave an overhang that you can use as handles to remove the brownies from the pan.  Set aside.
4. Make the crust: Stir the graham crumbs and the granulated sugar together in a bowl.
5. Pour the melted butter into the graham mixture, mixing until well incorporated.
6. Pour the graham mixture into the bottom of the prepared pan.
7. Use the bottom of a ¼ cup measuring cup to press the crust evenly in the bottom of the pan.  Set aside.
8. Make the brownies: Melt the butter and the chocolate together in a heat proof bowl placed over a saucepan of simmering water.  The bowl must not touch the water. Stir until combined.
9. While the chocolate and butter melt, beat the eggs, egg yolks, granulated sugar, brown sugar and salt together in the bowl of a stand mixer fitted with a paddle attachment on medium-high speed for 5 minutes.  The mixture will have doubled in size and turned a lighter colour.
10. Reduce the speed to low and pour in the vanilla, beating until incorporated.
11. Once the butter and chocolate have melted, remove the bowl from the heat and whisk in the cocoa powder.
12. Pour the warm chocolate mixture into the egg mixture and beat on low speed until incorporated.
13. Use a spatula to fold the flour into the batter.  Be careful not to overmix.
14. Pour the brownie batter into the prepared pan.
15. Push 16 evenly spaced marshmallows into the brownie batter.  Keep the top of the marshmallows above the brownie batter so that they get nice and toasty in the oven.
16. Crunch up the 2 graham cracker wafers with your hands and sprinkle the pieces over the brownies. 
17. Bake for 45 minutes, until a toothpick inserted in the middle comes out with a few moist brownie crumbs.
18. Place the pan on a wire rack and let cool completely.
19. Lift the brownies by the parchment paper overhang and place on a cutting board.
20. Use a large chef’s knife to slice the brownies into 16 portions.  Rince the knife in hot water and wipe it before each cut to get clean slices.
21. Store in an airtight container in the refrigerator for up to 3 days.