Put egg yolk in a mixing bowl and beat until light; gradually add the sugar and milk while beating continuously.
Sift your flour, baking powder, and salt together; set aside.
Beat egg white until stiff; fold dry ingredients into egg white.
Add egg white mixture and flavoring to sugar-milk mixture, blending well.
Pour batter in a prepared 8-inch square pan.
Bake at 375 degrees (a moderately hot oven) for 30 minutes.
For icing: Warm the 2 tablespoons evaporated milk in a small saucepan and add the 3/4 teaspoon lemon extract and 1 cup powdered sugar. Top on cake. If you like it, you can colour the icing with food colouring.