Prep. Preheat the oven to 350F. Get out a large baking tray (don't grease it or line it).
Make the dough. Add the butter, sour cream, and vanilla to a large bowl and cream together until smooth (you use a handheld electric mixer or do this by hand). Add the powdered sugar, flour, and salt, and stir to combine. The dough should be wet.
Pipe the dough. Immediately transfer the dough to a piping bag fitted with a large star tip (don't wait because the dough thickens as it sits due to the flour absorbing the liquid). Pipe the dough out into about 2 1/4-inch circles onto the baking tray, leaving about 2 inches between each cookie.(TIP/UPDATE: If your cookies aren't keeping their shape after baking, a brief chilling period should do the trick. After piping the dough onto the cookie tray, pop the whole tray in the oven for 20 minutes. After that, bake them directly from the fridge for 18 to 20 minutes. IMPORTANT: Don't chill the dough before piping because it will be too stiff to pipe.)
Bake. Bake until the cookies are light golden on the bottom, about 10 to 15 minutes.
Cool. Cool on the baking tray and then remove with a thin metal spatula.
Notes
Recipe Yield and Serving Size: This recipe makes 12 cookies; each serving is 1 cookie.
Make Them Extra Pretty: If desired, serve with a dusting of powdered sugar on top.
Storage: Store these cookies in an airtight container at room temperature for up to 5 days.
Freezing: You can freeze these cookies for up to 6 months. Wait to dust them with powdered sugar after they're thawed right before you're ready to serve them.
No Egg: You'll notice there's no egg in this cookie recipe; fear not, it's not a mistake. Here the sour cream acts as an egg replacement.
No Leavening Agent:There's also no leaving agent (such as baking powder or baking soda) in this recipe. Similar to shortbread (or brownies), we simply don't need it here.