Begin by lining a 15x10x1-inch baking sheet with aluminum foil. (You can use a 13x9-inch pan for thicker cookies.) Grease the foil with cooking spray. Also, preheat your oven to 375 degrees F.
In a large bowl, sift together the flour, baking powder, and salt. Set aside.
Cream together the butter and sugar until light and fluffy, about 3 minutes. Then, incorporate the egg, sour cream, and vanilla. Slowly add the flour mixture until well combined.
Very gently press the dough into the foil-lined baking pan. Bake for 14-17 minutes or until the edges are lightly golden. Allow to cool in the baking pan.
For the frosting, begin by creaming the butter. Then, slowly add the confectioners' sugar, alternating with half and half until you achieve the desired consistency. Then add the vanilla and almond extract along with the salt. Food coloring can also be incorporated at this time. (I used four different colors to create an ombre effect.)
Once the sugar cookie bars are cool, spread on the frosting. To achieve an ombre effect like I did, spread on the four different color frostings leaving about a half inch gap in between each. Then, blend them together. If desired, top with sprinkles before the frosting sets.