Preheat oven to 325°F. Spray two 18x13" sheet pans with nonstick spray, line with parchment paper, and spray again. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, combine the flour, sugar, cocoa powder, baking soda, baking powder, and salt. Mix on low speed until evenly combined.

In a medium bowl, whisk together the eggs, buttermilk, hot water or hot chocolate, vanilla extract, and vegetable oil until smooth.

With the mixer on low speed, slowly pour the wet ingredients into the dry ingredients. Mix just until combined. Scrape down the sides and bottom of the bowl with a rubber spatula to ensure everything is evenly incorporated.

Divide the batter evenly between the two prepared sheet pans—about 700g of batter per pan. Spread into an even layer, making sure it reaches all corners.

Bake for 15–17 minutes, or until the tops are set and no longer shiny. Let cool in the pans for 15 minutes, then transfer to the fridge to chill for at least 30 minutes.

Line a baking sheet with parchment paper.

Melt the dark chocolate in a large microwave-safe bowl in 30-second intervals, stirring between each until smooth.

Stir in the Rice Krispies until evenly coated.

Pour the mixture onto the prepared sheet and use a spatula to press it into an even layer. Sprinkle the top with flaky salt.

Place in the freezer to set. Once hardened, break or chop into small bite-size pieces. Set aside.

In a medium microwave-safe bowl, heat the heavy cream until hot and steamy—about 30–60 seconds. You want it to be hot enough to melt the chocolate.

Add the chocolate and let it sit undisturbed for 5 minutes.

Stir until smooth and glossy. If needed, microwave in 15–20 second bursts, stirring between, until fully melted.

In a stand mixer fitted with the paddle attachment (or in a large bowl with a hand mixer), beat the room temperature butter on medium speed for 3–4 minutes, until light and fluffy. Scrape down the bowl.

Add the powdered sugar, one cup at a time, mixing on low until mostly combined, then increasing to medium until smooth.

Pour in half of the prepared ganache (save the rest for the top of the cake), along with the vanilla and salt. Beat until creamy and fully incorporated, about 1–2 minutes.

If the buttercream is too thick, add a splash of milk or cream. If it’s too thin, add a little more powdered sugar.

Once the cakes are fully chilled, carefully trim the edges if needed and slice each sheet cake into 3 even strips, giving you 6 thin layers total.

Place a dollop of buttercream on a cake board or plate to secure the first layer. Add one cake strip and spread about ½ cup of buttercream evenly across the top using an offset spatula.

Sprinkle on a generous layer of chopped Rice Krispy bark and gently press it into the frosting.

Add the next cake layer and spread with raspberry jam or compote. Repeat this layering process, alternating buttercream + bark and jam, until all layers are stacked.

Once your cake is stacked and filled, use a serrated knife to carefully trim the sides to create an even rectangle. This helps clean up the edges and gives you that super polished bakery-style finish.

Once stacked, pour the remaining ganache over the top and gently spread it to the edges and down the sides with an offset spatula. You can go for a rustic swoopy finish or smooth it out—your call.

Top with rainbow sprinkles and extra Rice Krispy bark for crunch and color.

Chill for 20–30 minutes to set, then slice and serve!