Preheat the oven to 350°F (180°C). Line a 9x13 pan with parchment paper and set aside.
In a bowl, cream together the butter and sugar until light and fluffy.
Add in the eggs and cake batter flavoring and mix until combined.
Next, add in the flour, baking powder and sprinkles. Mix until thoroughly combined.
Press into the bottom of the lined pan.
Bake at 350°F (180°F) for 20-25 minutes. Or until the bars have puffed up, no longer look wet and glossy on the tops, and are just beginning to turn golden on the edges.
While the cookie bars are cooling, make the frosting.
Make the frosting by whipping the butter and cream cheese until smooth.
Add the powdered sugar, one cup at a time, mixing until combined.
Once all of the powdered sugar has been added, add the cake batter flavoring and milk, if needed.
Spread evenly on the cooled cookie bars and top with extra sprinkles, if desired.