Preheat oven to 325°F. Line a 1-inch tall 1/4 sheet pan with parchment paper, then spray the bottom and sides with cooking spray.

Sift flour, baking powder, baking soda, salt, instant pudding mix (or clearjel), and cocoa powder into a large bowl. Add both sugars and whisk until well blended, breaking up brown sugar clumps.

In a separate large bowl, combine eggs, buttermilk, coffee, oil, corn syrup, and vanilla. Whisk until smooth and well-blended.

Melt 3 oz butter in microwave until just melted. Add 1/4 cup chocolate chips and whisk until melted and smooth (30 seconds to 1 minute).

Pour wet ingredients into dry ingredients and whisk until incorporated. Pour chocolate butter mixture over batter and whisk until smooth and lump-free.

Pour batter into prepared pan and smooth until even. Let pan sit for 5-10 minutes before baking to allow instant clearjel to thicken batter.

Bake on middle or top rack at 325°F for 16 minutes. Without opening oven, reduce temperature to 300°F and bake another 6-10 minutes until toothpick comes out clean.

Once cool, wrap and freeze the cake in the pan for at least 2 hours or overnight.

For ganache, combine heavy cream and 1 cup chocolate chips in microwave-safe bowl. Heat in 30-second increments, stirring between, until smooth (2-3 heats total). Whisk in peppermint extract. Refrigerate until thick and fudgy, stirring occasionally.

For buttercream, whisk powdered sugar and clearjel together. Beat cream cheese until softened, add room temperature butter, then shortening. Slowly add powdered sugar mixture. Add vanilla and peppermint extract. Beat on high for 2-3 minutes until fluffy.

Reserve 1/4 cup ganache for drizzling. Cut frozen cake into layers using cake rings. Fill each layer with remaining fudgy peppermint ganache (about 1/4 inch high).

Apply thin crumb coat of peppermint buttercream on outside. Freeze for 10 minutes until firm.

Frost final coat of peppermint buttercream. Microwave reserved ganache until thin, then drizzle down sides using spoon or squeeze bottle.

Using pastry bag with 1M star tip, pipe tall rosettes around top of cake. Top with mini candy canes.

Refrigerate to set, but remove 2-3 hours before serving to bring to room temperature for best texture.