Set egg and butter outside to room temperature. Sift flour, baking powder and salt. Pre-heat oven to 350 degrees.
Cream the butter and sugar together, then add egg yolk one at a time. Set aside egg whites.Add flour alternating with milk to the mixture to form a thick but smooth batter.With a clean whisk, beat egg whites vigorously for 3-4 minutes or until it forms firm peaks.
Folding egg whites – Add half the egg white foam to the cake batter and mix slowly.Pour the rest of the egg whites in the middle of the batter. Mix it by ‘cut and fold’ motion from center (like turning burger patties).
Add vanilla extract and mix evenly. Grease the pan or use muffin liner and pour the cake batter and bake it for 40 minutes.Use a skewer to check if it had baked evenly and set on a grill to cool.