Preheat the oven to 350 F and line a 9 x 13 inch baking pan with aluminum foil, leaving an overhang to help lift the bars out.
In a large bowl, mix together the cream cheese and butter until smooth. Add the sugar, and cream together with an electric mixer, 2-3 minutes. Mix in the vanilla extract and egg.
Combine the flour, baking powder and salt in another bowl and stir into the butter mixture until well combined.
Press the dough evenly into the prepared pan and bake for 25-30 minutes, until just lightly browned on top. Transfer the pan to a wire rack and cool completely.
Remove the bars from the pan using the foil overhang.
Frost the bars with the buttercream and sprinkle with red and green sprinkles. Cut and serve.