Preheat your oven to 350 degrees. Line a 9 inch by 13 inch glass baking dish with parchment paper.
In a large bowl, cream together the softened butter and sugar with an electric mixer until fluffy, about two to three minutes. Scrape down the sides of the bowl as needed.
Crack the eggs into a small bowl and beat lightly. Add to the butter-sugar mixture along with vanilla extract, mixing until combined.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Gradually add into the wet mixture, mixing on low and then medium until a dough forms.
Fold in a quarter cup of the red and green sprinkles, mixing until evenly distributed.
Transfer the dough into the prepared pan, spreading evenly with a rubber spatula or clean hands.
Bake in the preheated oven for 25 to 27 minutes, until edges are golden. Cool for 20 to 30 minutes in the pan.
While cooling, prepare the frosting by beating softened butter for three to four minutes. Add vanilla and salt, mixing until well combined.
Gradually add powdered sugar, mixing until smooth and fluffy. Frost the cooled cookie bars and decorate with additional sprinkles.
Trim the edges for a neat finish and slice into even pieces before serving.
