In a mixing bowl, add the softened butter and sugar. Blend with a mixer until fluffy.
Add the vegetable oil, heavy cream, and vanilla. Blend again until creamy.
Sift in the cake flour, cream of tartar, baking powder and salt.
Fold everything together until combined and a thick dough forms.
Cover in plastic wrap and refrigerate for 1 hour.
Preheat the oven to 350 degrees Fahrenheit. Line a cookie sheet with parchment paper.
Use a 2 inch scooper to scoop the chilled cookie dough onto the baking sheet. Space each dough ball about 2 inches apart from each other.
Bake for 12 minutes or until the cookies are set and are barely browned at the edges.
Let cookies cool completely.
While the cookies bake, make the frosting.
In a mixing bowl, add the butter and blend with a hand mixer until fluffy and the color has paled.
Add the powdered sugar and salt, then blend again until incorporated. The frosting may still be crumbly at this point.
Add the vanilla and heavy cream and blend until the frosting is creamy.
Dye with pink or blue food coloring to achieve desired color.
Transfer to a piping bag and snip a large hole at the end.
Frost the cooled cookies by creating a thick large swirl from the center to the edges. Then smooth the harsh lines with a butter knife. Repeat with all the cookies and top with colorful sprinkles of choice.
Notes
Store cookies in a tightly sealed container, or Ziploc bag, at room temperature for up to 5 days