Preheat oven to 350°F (175°C) and line a baking pan with parchment paper.
In a bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the eggs one at a time, then stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Stir in the Christmas sprinkles and chocolate chips (if using).
Press the dough evenly into the prepared baking pan.
Bake for 20-25 minutes, or until the edges are golden brown and the center is set. A toothpick inserted into the center should come out with moist crumbs attached.
Let the bars cool completely in the pan before cutting them into squares.