Make a heart stencil that is approximately 7” (18cm) wide and 7” (18cm) long. I use a regular A4 piece of paper.
Crack the egg into a mixing bowl and add in vanilla extract. Set aside.
In a heavy-bottomed medium saucepan, add the butter, honey, and sugar. Heat over medium heat until the butter has melted and the mixture starts simmering.
Lower the heat to low and add baking soda. Whisk to combine. The mixture will bubble and expand a lot but will then subside. Cook over low heat, stirring continuously to prevent the honey from burning, until the mixture turns a light amber color.
Remove from the heat and slowly pour the honey mixture into the bowl with the egg, whisking continuously.
Add red food coloring and mix well to incorporate.
Then, sift in the flour, cocoa powder, and salt, and mix until no dry ingredients are left. The dough should be sticky, so don’t add more flour! Wrap the dough in plastic wrap and place it in the fridge for 1 hour, or overnight.
Preheat the oven to 180C (355F). Prepare a baking sheet and 5 pieces of parchment paper.
Split the dough into 5 even parts (around 85g each). Take one piece and place it on parchment paper, cover it with a piece of plastic wrap, and roll it out. If it sticks to the parchment paper, lift the dough slab, flip it cover it with the plastic wrap again, and keep rolling. The final slab should be around 2-3mm thick, and you should be able to cut out a heart shape using the stencil that you have prepared. Do not cut it out yet.
Bake each layer for 5 minutes or until puffy and no longer shiny. Take the baking sheet out of the oven. Lift the baking paper with the cake layer and remove it from the baking sheet.
Cut out the heart shape using the stencil and a small sharp knife. Place the leftovers on a separate plate. We will use them to decorate the cake.
Transfer the cake layer onto a cooling rack. Don’t stack baked cake layers on top of each other if they’re still warm.
Roll out, bake, and cut out the rest of the cake layers.