Step #2 Grease only the bottom of a 9-inch round cake pan & cover with a circle of parchment paper.
Step #3 Do not grease the sides of the pan.
Step #4 In a large bowl, beat egg yolks until light, slowly adding in the sugar.
Step #5 Add in vanilla & lemon & set aside.
Step #6 In a medium bowl, about 1 min at high speed, beat the egg whites until frothy, then beat in the salt & cream of tartar.
Step #7 Continue beating until the eggs reach soft peaks.
Step #8 Fold egg whites, working in 3 or 4 batches, into the yolk mixture.
Step #9 Sift the flour over the egg mixture, pour this into prepared cake pan & bake unil a tester comes out dry & the top of the cake springs back when carefully pressed, & carefully fold it inches When the batter is uniform, again working in 3 or 4 batches, about 35-45 mins.
Step #10 Allow cake to cool in the pan before cutting around the sides with a sharp knife & turning it out.
Step #11 Slice the cake into 2 or 3 layers (or squares) & fill as desired.