Preheat the oven to 375 degrees Fahrenheit.
In a large mixing bowl, cream together your butter and sugar for about 3 minutes until light and fluffy.
Add in your egg, vanilla, and cream cheese and mix until they are combined.
In a medium sized bowl, whisk together your flour, baking powder and salt.
Fold the Christmas sprinkles into the batter.
Slowly add in your flour mixture into the wet mixture, while stirring until everything is combined.
Press the batter into a greased 9×13 baking dish and spread it out evenly with your hands or a rubber spatula.
Bake for 15-17 minutes or until edges just barely start to turn golden.
Allow the bars to cool completely.
Mix together all your ingredients for your frosting until fluffy creamy.
Add in desired amount of food coloring.
Spread frosting evenly over cooled cookie bars.
Top with sprinkles, or Christmas m&ms, as desired.
Cut into squares and serve.