Weigh or measure the powdered sugar into a bowl and set it aside. Next, weigh or measure the flour and baking powder in another bowl. I run a whisk through to blend.
Cream the butter and cream cheese together for a couple of minutes. Scrape the bowl down and add the powdered sugar. Start on the lowest mixer speed until incorporated, then turn the mixer to medium speed for 2 to 3 minutes. Add the egg and add the vanilla extract, and blend until incorporated. Complete the dough by slowly adding the flour mixture a quarter at a time. Do not over-mix the flour. You can always finish using a spatula. Chill the dough for 1 hour.
While you prepare the cookies, preheat the oven to 350°F (175°C or 180°C). Line two cookie sheet pans with parchment paper.
Take the cookie dough out of the refrigerator and, using a medium cookie scooper, shape a scoop of dough into 1 ½-inch balls. Roll the balls around the superfine sugar and place them about 1 ½ inches apart. I take two fingers and lightly press on the top of each ball to flatten it a little.
Bake for 10-12 minutes. They will look white with just a hint of golden brown along the edges. They may look underdone, but leaving them on the cookie pan for about a minute helps to firm them up. At this point, move them to a cooling rack to finish.
When completely cooled, I add a little powdered sugar to a small sifter and lightly dust each cookie. Store in an air-tight container for 3-5 days.