Preheat oven to 375 degrees F. Line a 9x13" baking pan with parchment paper and spray with cooking spray. Set aside.
First combine dry ingredients (flour, baking powder, and salt). Set aside.
In the bowl of a stand mixer with paddle attachment (or in a large bowl with a handheld mixer), beat together butter and sugar until light and fluffy. Beat in egg and egg white, and vanilla until well combined.
Slowly add dry mixture and mix until well combined. Turn dough out into baking pan and press mixture into pan. Bake 14-15 minutes until edges have the lightest brown color. Then remove from oven. Cool completely, then frost.
Beat butter in a stand mixer with paddle attachment until softened and smooth.
Add in 1 c. of powdered sugar, then a tiny bit of milk, beat on high until smooth. Continue this process until all the powdered sugar is incorporated and frosting is smooth. Add vanilla extract and almond extract, and beat until smooth.
Spread frosting on top of cooled bars. Cut and serve! Store bars in an airtight container so they don't dry out.