1 Combine the dry ingredients: Whisk the flour, baking powder, baking soda, and salt together in a bowl and set to the side.
2 Make the cookie dough: In the bowl of a stand mixer with a paddle attachment, beat butter and sugar together until light and fluffy, about 3 minutes. Beat in the eggs one at a time, scraping down the bowl after each addition.
Beat in the vanilla and sour cream until combined. Then, in two separate additions, beat in the flour, scraping the bowl after each addition. This will create a soft and fluffy dough.
3 Fold the dough briefly in the bowl: Using a stiff rubber spatula, fold the dough a few times inside the bowl – scoop down the side of the bowl and underneath the batter, then lift up and fold the dough over on itself. Give the bowl a quarter turn and repeat. Repeat this a few times until the dough is smooth.
4 Chill the dough: Press a piece of plastic wrap against the surface of the dough and refrigerate the dough for at least three hours so it firms up, or up to overnight. (Transfer the dough to a separate bowl if you need the mixing bowl for something else.)
5 Preheat the oven: Once the dough has chilled and you’re ready to bake, preheat the oven to 350°F with a rack in the center position. Line two baking sheets with parchment paper.
6 Shape the cookies: Lightly flour the counter. Using a medium (1 1/2 tablespoon) cookie scoop, scoop out some of the dough and drop on the counter. Gently roll the dough against the counter and between your hands to form a round ball. Brush off any excess flour and place the ball on the cookie sheet.
Repeat scooping and rolling more cookie dough balls until the sheet pan is filled, spacing the cookies several inches apart. Cover the remaining dough and return it to the refrigerator.
7 Press the cookies flat: Dip the bottom of a drinking glass in flour and use it to press the cookies on the cookie sheet to about 1/4-inch thick. Re-flour the drinking glass as needed to prevent sticking.
8 Bake the cookies: Bake the first tray of cookies in the center of the oven for 11 to 13 minutes. When done, the cookies should be slightly puffed, dry on the top, pale around the edges, and (when lifted with a thin spatula) barely golden on the bottoms.
Let them cool for 5 minutes on the tray before transferring them to a wire rack to cool.
Shape and bake the remaining cookies like the first.
9 Make the frosting: Using the paddle attachment, beat the butter in the bowl of a stand mixer until creamy. Add half of the powdered sugar, the vanilla, and the salt, and beat on low to combine for a minute. Add the remaining powdered sugar and 1 tablespoon of milk, and beat for an additional minute.
The frosting should be fluffy, pale, and spreadable. If it is more stiff than you like, beat in an additional tablespoon of milk.
To color the frosting pink (or any other color), add a few drops of food coloring and mix to combine. (I used about 2 drops each of deep pink and red food gel for my cookies.)
10 Frost the cookies: Spread the frosting on the cooled cookies and decorate with sprinkles.
11 Store the cookies: These cookies keep well in an airtight container at room temperature for up to 3 days, separated by layers of parchment so they don’t stick to each other.