Preheat oven to 325 degrees. Sift flour before measuring. Combine and sift with sugar. Beat egg yolks until light and thick. Slowly add half of the sugar, continuing to beat at medium speed of electric mixer. Stir in grated lemon rind and vanilla. In a separate bowl, add a pinch of salt, and cream of tartar to egg whites; beat whites with a wire whip until stiff enough to stand in peaks, but not dry. Into the egg yolk mixture, gently fold remaining sugar and then egg whites. Next, fold in the flour and salt, and then, the remaining egg whites. Pour the batter into an ungreased tube pan. Bake for about 1 hour or until cake tests done. Remove from oven and invert pan until cool. Using a dull knife, run it around the edge of the pan to separate cake from pan if required.