A home-kitchen take on Sarawak layer cake — moister and softer, with a much lower failure rate than the classic.
Let the butter soften at room temperature until a finger leaves an indent.
Line the tin with baking paper and bring a steamer of water to a boil.
Beat the softened butter on high speed until pale and fluffy.
Add the eggs one at a time, beating each in fully before adding the next.
Add the kaya and condensed milk and mix until smooth.
Sift in the cake flour and beat until the batter is smooth with no lumps.
Divide the batter evenly between two bowls.
Bowl A (Horlicks layer): stir in the Horlicks powder.
Bowl B (dark layer): stir in the cocoa powder.
Layer 1: spread 200g of batter level in the tin, cover with foil and steam over medium-high heat for 5–7 minutes, until the surface is set and no longer sticky.
Continue with 200g per layer, alternating colours, steaming each layer 5–7 minutes over medium-high heat until the batter runs out (about 10 layers).
Remove and cool completely in the tin, about 3 hours, then chill at least 4 hours before slicing.