Preheat the oven to 350ºF. Spray a 9x13 baking pan with non-stick cooking spray or line it with non-stick aluminum foil or parchment paper.
Add butter and cream cheese to the bowl of your electric mixer. Beat until smooth. Stop the mixer and scrape the side. Add the sugar and mix until combined.
Stop the mixer and scrape the sides again before adding the egg and the vanilla. Mix well after the addition. Next, add the flour, baking powder, and baking soda. Mix until combined.
Spread the dough evenly in the pan and smooth the top. Bake for 16 to 20 minutes. I baked mine for 18 minutes. Allow the cookies to cool completely before frosting.
In the bowl of your stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy. Stop the mixer and scrape the sides.
With the mixer on low, add the powdered sugar, cream, and vanilla extract. Once the sugar is mixed in, you can turn the mixer speed up to medium and beat until the frosting is fluffy (about 2 minutes).
You can always add more sugar if frosting is too thin or more cream if the frosting is too thick.
If you want to color the frosting, add the food coloring and mix until it's combined.
Spread the frosting on cooled sugar cookies. Decorate with sprinkles if desired.
Store the bars in an airtight container on the countertop up to 2 days or in the refrigerator up to 5 days.