Pre-heat the oven to 195 to 200 degree Celsius.
Sift flour and spices together.
Butter mixture: Beat frozen butter and condensed milk till white, then set aside.
Egg mixture: Whisk egg whites and baking powder till stiff at medium speed. Add in sugar, then egg yolks one by one.
Stir in flour into the egg mixture (I used hand folding).
Mix in butter mixture into egg mixture in 3 rounds using a whisk (I used hand folding).
Mix in rum till blended in.
Line a square baking tin with paper, grease the paper well.
Heat the tin for 2 minutes in the heated oven.
Weigh out 130 g of batter and spread onto the baking tin. Bake the first layer till well browned.
Turn the oven to grill mode. Place a second layer of 100g and grill this second layer till brown. Repeat the grilling process for all subsequent layers of 100g each, till all the cake batter is used up.
Between each layer, press the cake down well using a lapis press.
