Preheat oven to 350° F. Line a baking sheet with parchment paper and set aside.
In a medium bowl, whisk together flour, baking soda and salt. Set aside.
In the bowl of a stand mixer (or using a hand mixer), beat butter and sugar on medium-high speed until light and fluffy, about 3 minutes. Scrape down the sides and bottom of the bowl halfway through.
Add egg, egg yolk and vanilla. Mix until combined, about 30 seconds.
With the mixer on low, slowly add the flour mixture to the bowl. Mix just until combined. Batter will be thick. Use a spatula to scrape the bottoms of the bowl to ensure all flour bits are mixed in.
Use a medium cookie scoop to scoop about 1 ½ tablespoons of dough. Use your hands to roll dough into a ball and roll each ball in remaining 2 Tablespoons sugar. Repeat with remaining dough, placing each ball about 2 inches apart on the prepared baking sheet.
Bake cookies 350° F for 8 to 10 minutes or until the edges are set, but not yet brown. The centers of the cookies will be soft and pillowy (they will fall as they cool). Let cookiex cool on the pan for 5 minutes, then transfer to a wire rack to cool completely.
Notes
High altitude adjustments: Decrease granulated sugar by 2 Tablespoons.Storing sugar cookies: Store sugar cookies in an airtight container at room temperature for up to a week.Freezing sugar cookie dough: Wrap sugar cookie dough in plastic wrap and freeze for up to 3 months. Defrost in the refrigerator before rolling into balls and baking.