Preheat your oven to 350°F (175°C). Line your 9x13-inch baking pan with parchment paper or grease it well to prevent sticking.
In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, use an electric mixer to beat the softened butter and granulated sugar until light and fluffy, about 2-3 minutes.
Beat in the egg and vanilla extract until fully combined.
Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined. Avoid overmixing to keep the bars soft.
Press the cookie dough evenly into the prepared pan, smoothing the surface with a spatula.
In a separate bowl, beat the softened cream cheese, powdered sugar, and vanilla extract until smooth and creamy.
Gently spread the cream cheese mixture over the cookie base, covering it evenly.
Sprinkle your favorite colorful sprinkles over the cream cheese layer. Bake in the preheated oven for 25-30 minutes, or until the edges are golden and the center is set.
Allow the bars to cool completely in the pan before slicing into squares. This helps the layers set for clean cuts.