Preheat the oven to 180 C / 350 F. Butter and flour a 8 inch square pan , line the bottom with parchment.
Separate the eggs .
Whisk together the flour and baking powder in a bowl, keep aside.
Beat the whites using an electric mixer or whisk until stiff peaks form. This takes 2-3 minutes.
Add the yolks little by little while continuing beating.
Once the yolks are incorporated , add the sugar one tablespoon at a time while continuing beating.
Beat for a minute or two after the last of the sugar is added.
Beat in the vanilla.
Sift in the flour- baking powder mixture on top of the batter.
Using a spatula, gently fold in the flour until you can't see flour anymore .
Immediately pour batter into prepared pan and smooth the top.
Bake at 180 C / 350 F for 25- 30 minutes until the cake springs back when touched and the edges are coming away from the pan sides.
Cool in pan for 10 minutes . Remove and cool completely on wire rack.