Preheat oven to 360 F. In a bowl add flour, lemon zest, salt and baking powder. Stir with a whisk.
In another bowl blend with whisk attachment on low your soft butter and brown sugar. Add the eggs one at a time to the butter bowl, then vanilla and lemon extract. Blend until smooth.
Add dry ingredients in portions, as well as milk. The dough should be smooth without lumps. Line a 9x13" baking dish with parchment paper and place the batter inside. (if you want it thicker than 2" in the middle, put into a 9x9 pan instead) Bake for 30-35 minutes or until middle bounces back when touched gently.
Cool the finished cake without removing it from the baking dish. Beat the egg whites for two minutes with a whisk attachments with electric mixer, then add sugar in portions and make a fluffy dense meringue. The whisk should have strong meringue peaks.
Transfer the meringue to a piping bag fitted with a star nozzle. Pipe the meringue on to the surface of the cake.