Preheat oven to 350 degrees F.
Grease and flour two 9" round cake pans.
In medium bowl, combine flour, baking powder, and salt, and stir to combine.
In small bowl, combine ¼ cup of the sugar with the lemon zest, stirring until zest and sugar are completely combined.
In large bowl with electric mixer, beat lemon sugar with butter until light and fluffy, about 1 minute.
Add the remaining 1 ½ cups of the sugar and beat until smooth, about another minute.
Add ¼ cup of the milk and beat in until just combined.
Then add a quarter of the flour mixture, beating until just combined. Repeat with remaining milk and flour mixture until all of it is added to the batter. Don't over mix.
In a separate bowl, beat the egg whites until foamy.
Add cream of tartar, then beat on until stiff peaks form.
Fold in the egg white mixture gently, ⅓ of it at a time, being careful not to deflate the mixture.
Pour batter into the prepared cake pans, dividing evenly, and smoothing the tops with a spatula.
Bake in preheated oven for 35-40 minutes, until a cake tester comes out clean. Mine took 35 minutes.
Let cool in the pans for 10-15 minutes, then carefully invert each cake onto a cooling rack. Cool completely.