Preheat the oven to 325°F or 160°C. Line a 6-inch cake pan with parchment paper.
Heat the egg mixture to 104°F or 40°C. In a medium-sized heat-proof bowl, add the egg, granulated sugar, and honey. Place the mixing bowl inside a large stainless steel bowl and fill it with hot water. Using a hand mixer whisk the mixture on low-medium and bring the temperature to 100-105°F. (This will melt the sugar and allow the batter to gain volume easier.
Whisk air into the egg mixture. Once it reaches 104°F or 40°C take it out of the water bath and continue mixing on high until the batter is pale yellow/ivory and the volume has increased. To test if it's the right consistency you should be able to lift the batter and produce a trail on top of the mixture, if it holds its shape it is ready. Or you can stick a toothpick in and if it holds then it is ready.
Tighten the air bubbles. Once you achieve the right consistency, take the hand mixer and whisk gently on low to remove all the large air bubbles for about 1-2 minutes. The final result should be smooth and silky.
Sift in the flour. Sift in the flour and fold it in gently. Be careful not to remove all the air by over mixing. Stop immediately when it is combined.
Melt the butter in the milk. In a small saucepan, heat the milk and butter over low heat and mix until the butter has melted and reaches 140°F or 60°C. Place in a small heat-proof bowl.
Add the butter mixture into the batter. Take a small amount of the egg batter and mix it in the small bowl of the butter mixture. This cools down the butter and milk and creates less shock to the batter. Then pour this into the original batter and gently fold until combined. Do not over mix.
Transfer to the cake pan, tap the cake pan on the workspace once to release air bubbles, and bake at 325°F or 160°C for 30-35 minutes. Test to see if the cake is ready by poking the center with a toothpick.
Once you take it out of the oven, tap the cake down onto the workspace again to prevent the cake from collapsing as it cools. Remove the cake and turn the cake upside down to cool for 10 minutes.
Let the cake cool completely before slicing the cake into 3 sections of about 1.5 cm each.