Cut the butter into cubes and leave on the kitchen counter for an hour or until they reach room temperature. You may alternatively heat the butter in the microwave for 30 seconds.
2
Whisk butter and sugar until fluffy.
3
Separate the egg yolks from the egg whites.
4
Whisk one egg yolk at a time into the butter and sugar mixture.
5
Fold in the flour and baking powder little by little.
6
Grate half of the lemons and add to the mixture together with the lemon juice (Note: Set aside a few tablespoons of lemon juice for the icing).
7
Beat egg whites in another bowl until white and you see stiff peaks starting to form. Then, gently fold the egg whites into the cake batter with a spatula.
8
Pour the cake batter into a baking tin lined with baking paper. The cake batter should fill about half of the tin.
9
Bake in the middle of the oven at 180 degrees celsius for about 30-40 minutes. Cool on a rack.
10
Make the icing by mixing the icing sugar with lemon juice. Add one teaspoon at a time of lemon juice until you have the perfect icing consistency. Add more icing sugar if it becomes too runny.
11
Top the cooled-down cake with icing, and decorate with thin slices of fresh lemon.
