Beat the butter with the sugar and the freshly grated lemon peel with an electric beater or in a stand mixer fitted with the whisk attachment;
Add the butter and sugar alternately and beat for at least 15 minutes until creamy and fluffy;
Slightly beat one egg at a time and pour it into the mixture; add another egg when you have incorporated the previous one. Beat the mixture at a low speed until fluffy and smooth;
Sift the flour, the potato starch, the baking powder, and the salt; mix in a spoonful of flour at a time. The flour has to be completely incorporated before adding another spoon. Continue to beat with the paddle attachment until smooth and creamy;
Pour the batter into a 9-inch (24cm) springform pan lined with parchment paper;
Pre-heat the static oven to 350°F (180°C) and bake for about 40 minutes. Be careful not to open the door until the surface becomes golden brown;
Insert a toothpick into the center of the cake: if it comes out clean, your cake is done;
While still hot, release the side of the springform pan and place the cake upside down onto a large flat serving plate, peel away the parchment paper; let it sit for about 15 minutes (otherwise it will get too moist);
Invert the cake back onto a cooling rack;
Let it cool completely and then generously sift powdered sugar all over the top of the cake.