• Preheat oven to 350°F. Butter a 9x13-inch baking pan.

Make the Cake Batter:

• In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt until evenly combined.
• In a separate bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla until smooth. Slowly add the wet ingredients to the dry ingredients, stirring as you go. Once the batter starts to come together, pour in the hot coffee and stir just until fully combined, scraping the bottom of the bowl.

Bake the Cake:

• Pour the batter into the prepared pan and bake for 35–40 minutes, or until a toothpick inserted into the center comes out clean.
• Let the cake cool in the pan for about 30 minutes. Using the back of a wooden spoon, poke holes all over the cake, about 2 inches apart.

Make the Nutella Soak:

• In a microwave-safe bowl, heat the heavy cream until just steaming and bubbling around the edges, about 45 seconds. Stir in ⅓ cup Nutella and the salt until smooth.
• Pour the mixture evenly over the cake, making sure it seeps into the holes and spread across the surface.

Make the Crunch Topping:

• In another microwave-safe bowl, melt the chopped chocolate in 20-second increments until it’s partially melted. Add in the butter and continue heating in 20 second increments, stirring between each until combined and smooth. Stir in the ½ cup Nutella and until fully melted.
• Add the crushed cornflakes in increments and gently stir until evenly coated.

Assemble & Serve:

• Spoon the chocolate cornflake mixture evenly over the cake, gently spreading into an even layer.