After combining the flour, salt, and nutmeg in one bowl, beat the butter, sugars, and orange zest in another bowl. Here, I chose orange zest, but you can also use lemon zest as well.
Once beaten, add the egg, egg yolk, and vanilla until well combined.
Gradually add the dry ingredients. Once all mixed together, the batter will be very thick!
Spread the batter into the prepared pan. For an even surface, cover the dough with plastic wrap and smooth down the surface.
