Using a hand or stand mixer, cream together butter and cream cheese until smooth and fluffy, about 3 minutes.

Add sugar, salt, egg, and vanilla extract to the butter and cream cheese mixture. Mix on medium-high speed until well combined.

Gradually add the flour and baking powder, mixing slowly at first and then more thoroughly until a soft dough forms. Do not overmix.

Divide the dough in half, flatten each into a disk, wrap in plastic wrap, and refrigerate for at least 1 hour.

Preheat oven to 375°F (190°C). Line baking sheets with parchment paper. Lightly flour a clean surface and roll out one dough disk to 0.25 inches thick.

Cut cookies into shapes using cookie cutters and place on prepared baking sheets about 1 inch apart.

Bake for 8-9 minutes, or until the edges just begin to turn golden. Cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

In a medium bowl, combine powdered sugar, heavy whipping cream, light corn syrup, vanilla extract, and 2 tablespoons of water. Whisk until smooth. Add extra water, 1 tablespoon at a time, until icing reaches a pourable consistency.

For colored icing, use a toothpick to add gel food coloring and mix thoroughly until desired shade is achieved.

Transfer icing to a ziplock bag, cut off a small corner, and drizzle over cooled cookies. Decorate with sprinkles before icing sets.