1. Start the Dough: In a large mixing bowl, using either a hand mixer or a stand mixer, beat the softened butter and granulated sugar together on medium-high speed until the mixture looks wonderfully light and fluffy.
2. Add Wet Ingredients: Beat in the large egg until it's fully combined. Then, reduce the mixer speed to low and stir in the sour cream and pure vanilla extract (and almond extract, if you're using it). Mix until everything is well incorporated, making sure to scrape down the sides of the bowl with a silicone spatula.
3. Combine Dry Ingredients: In a separate medium bowl, sift together the flour, cornstarch, baking powder, baking soda, cream of tartar, and salt. Give these dry ingredients a quick whisk to ensure they're evenly mixed.
4. Finish the Dough: With your mixer on low speed, slowly add the combined dry ingredients to the wet mixture. Mix just until no dry streaks of flour remain; be careful not to overmix the dough.
5. Chill Time: Cover the bowl tightly with plastic wrap and place it in the refrigerator to chill for at least 1 hour. This step is super important for making the dough easier to handle and helps create those perfectly soft cookies.
6. Preheat & Prep: Preheat your oven to 375°F (190°C). Line two baking sheets with parchment paper – this makes cleanup a breeze!
7. Shape the Cookies: Take half of the chilled dough from the fridge. For each cookie, scoop about 1 tablespoon of dough and gently roll it into a smooth ball. Place the dough balls onto your prepared baking sheets, leaving about 2 inches of space between each. Then, use the bottom of a glass cup or the back of a large spoon to gently press and flatten each ball into an even disc.
8. Bake to Perfection: Bake on the middle rack of your preheated oven for 9-13 minutes. Watch them closely: the cookies are ready when the edges just begin to turn a very light golden color (they should definitely not be brown). If you're baking with two sheets, remember to switch and rotate them halfway through for even cooking.
9. Cool Down: Once baked, remove the cookies from the oven and let them cool completely on the baking sheets. They'll continue to set and firm up as they cool. Repeat the shaping and baking process with any remaining dough.
10. Whip up the Frosting: While the cookies cool, prepare your frosting. In a clean mixing bowl, beat the softened butter with your mixer for about 3 minutes until it becomes wonderfully light and fluffy.
11. Sweeten the Frosting: Add the pinch of salt and vanilla extract. Then, slowly add about 2 cups of the powdered sugar, beating until the mixture is smooth.
12. Achieve Perfect Consistency: Gradually add 1 tablespoon of heavy cream at a time, continuing to beat. Add the remaining powdered sugar until your frosting reaches your desired smooth consistency and taste (you might not need all of the sugar or cream). If you want to color your frosting, add food coloring now and mix until evenly distributed.
13. Decorate & Enjoy: Once your cookies are completely cool, spread a generous layer of frosting on each one. If you're using them, sprinkle with colorful candy sprinkles. Let the frosting set slightly, then they’re ready to enjoy!