Preheat oven to 350 degrees and line a 9 x 9 pan with parchment paper.

Cream the butter using a stand mixer or a hand-held mixer until light and fluffy. Add in both sugars and beat for an additional two to three minutes or until well blended. Add in egg, egg yolk and extracts and mix until incorporated.

Sift in flour, baking powder and salt and mix until just blended.

Transfer dough to lined pan and spread until even (I find using a damp spatula helps as the dough is sticky).

Bake in preheated oven for 22-25 minutes or until just barely golden brown. Set aside to cool completely.

To make the frosting, beat butter until light and fluffy. Sift in confectioners sugar and mix. Add in milk one tablespoon at a time, adjusting as necessary until you get a thick but spreadable consistency. Add in extract and frost cooled bars.