Instructions for the sponge

• Preheat oven to approximately 190 degrees Celsius and line two baking trays with baking paper.
• Combine milk and vinegar in jug and set aside for 15 minutes.
• Beat butter, vanilla and sugar in a large bowl with a handheld of stand mixer. 
• Add milk mixture, baking powder and flour to the bowl, and mix with a spatula until just combined. 
• Spread mixture evenly in baking trays and bake for approximately 15 minutes, or until the sponges spring back when touched. It may take less or more time depending on your oven, so be sure to monitor them. 
• Remove sponges from the oven and set aside to cool.

Instructions for the croustillant

• While the sponges cool, place cornflakes, pecans and pretzels into a food processor and blend until mixture resembles thick breadcumbs. A few chunks are okay, but the majority of the mixture should be fine. 
• Melt chocolate in a medium sized bowl, then add cornflake mixture and mix to combined.
• Place a large piece of baking paper over the top of one of the sponges and flip it (the top of the cake should now be what was the bottom in the oven). 
• Remove the baking paper from the top of the sponge and spread croustillant over its surface. 
• Place a piece of baking paper over the croustillant and place the sponge into the fridge to set. Set the remaining sponge aside. 

Instructions for the coffee syrup

• Heat water, sugar and coffee in a small saucepan until mixture is well combined and starts to bubble. 
• Place a large piece of baking paper over the top of one of the sponges and flip it (the top of the cake should now be what was the bottom in the oven). 
• Brush the top of the cake with half of the coffee syrup and place in the fridge. 
• Remove the other sponge from the fridge, brush with remaining syrup and place into the fridge to set. 

Instructions for the buttercream

• Place all ingredients into a large bowl and beat with a handheld or stand mixer until smooth.
• Remove the croustillant sponge from the fridge and spread the buttercream evenly over the coffee syrup surface. 
• Place back into the fridge to set. 

Instructions for the ganache

• Heat milk in a small saucepan until it's hot but before is starts to boil.
• Add chocolate and butter and mix until all of the chocolate has melted and mixture is smooth. 

Instructions for assembly 

• Remove both sponges from the fridge. 
• Remove the baking paper from the croustillant sponge and place it (croustillant side down) onto your a large tray or board.
• Place second sponge onto buttercream side of the first sponge. 
• Spread ganache over the top sponge, using a hot knife to smooth the surface. 
• Place opera cake into the fridge to set for at least 2 hours.
• Once the opera cake has set, cut into pieces, decorate as desired and serve. Store in the fridge in an airtight containers.