• Preheat the oven to 350 degrees F (or 325 degrees F for convection bake). Line several half sheet pans with parchment paper.
• In the bowl of a stand mixer fitted with the paddle attachment (or in a bowl using a handheld electric mixer), add the butter, oil, granulated sugar and powdered sugar.

  Sprinkle the baking soda, cream of tartar, and salt across the top of the sugars Mix until well-combined and super creamy, 1-2 minutes, scraping down the sides of the bowl as needed.
• Add the sour cream, eggs and vanilla and mix until well-combined, 1-2 minutes, again scraping down the sides of the bowl as needed.
• Add the flour and mix until no dry streaks remain and the mixture is evenly combined; don't over mix.
• Scoop the dough into about 3-tablespoon sized portions (I use a #20 cookie scoop) and roll into balls.

  Place several inches apart on the prepared baking sheets.

  Add about 1/2 cup granulated sugar to a shallow dish or bowl.

  Lightly spray the bottom of a flat-bottomed glass with cooking spray and dip the bottom of the glass into the sugar. TIP: I prefer Baker's Joy Baking Spray. Spray a flat dish with the spray (much easier and less messier than spraying the bottom of a glass repeatedly.)

  Press each cookie into an even thickness dipping the bottom of the glass into the sugar between each press, as I found was necessary. Twist the glass to release from the pressed cookie. The edges of the cookie should look ruffled on the edges. The thickness of the cookie should be between ¼ and ½ inch. NOTE: I found that the cookies don't spread all that much.
• Bake the cookies for 10-12 minutes until just set. (Mine took 17 minutes.) Gently touch and slightly lift the edges a cookie. If it feels firm and set, the cookies are done. If the cookies are golden on the edges, that means they've baked too long. They might be dry and crumbly instead of creamy and soft.
• Let the cookies cool for a few minutes on the baking sheets before removing to a cooling rack to cool completely.

For the frosting:

• Using a handheld or stand mixer, combine the butter, sour cream and vanilla (or almond extract). Mix until thick and smooth and creamy, 1-2 minutes.

  Add the powdered sugar and cream (or milk) and mix until well-combined and creamy, scraping down the sides of the bowl as needed.

  Add food coloring, if using, then add additional cream, if needed, to adjust the consistency of the frosting so it is thick but still soft and spreadable.
• Frost the cooled cookies and decorate with sprinkles, if desired.
• TIP: I filled a pastry bag with a #12 large round piping tip. With each cookie I piped a mound of frosting, then used a small off set spatula to spread the icing.