Preheat oven to 350°. Cream butter, sugar, egg and yolk, plus extract until smooth, about 30 seconds. Add flour and baking powder and mix well. Dough should be soft but not sticky. 

Do not chill dough ~ roll out in one big or several smaller batches, to about ½ inch thick. Cutout cookies in whatever shapes you desire, and bake for 6-8 minutes. Allow cookies to cool completely before frosting. You can place them in the freezer to speed this process up. 

In a small bowl combine all ingredients and combine with a hand mixer or standing mixer for about 30-45 seconds. Frosting should be smooth and lump free. Spread or pipe frosting onto cookies. Sandwich with a second cookie. 

Store in an airtight container at room temperature for up to four days.  Enjoy!