Preheat
Preheat oven to 350°F. Line baking sheets with parchment paper.
Mix the Dry
In a medium bowl, whisk together flour, baking powder, and salt.
Cream the Butter & Sugar
In a large mixing bowl, beat butter and 1 1/4 cups sugar on medium-high until light and fluffy (2-3 minutes). Scrape down the sides as needed.
Add the Wet
Beat in the egg, egg yolk, and vanilla extract until fully combined.
Add the Dry
Gradually beat in the flour mixture until a dough forms.
Shape & Roll
Roll dough into balls using a large (3 tbsp) cookie scoop. Roll each ball in the remaining 1/4 cup sugar. Place on baking sheets 2 inches apart. Slightly flatten each ball with the bottom of a measuring cup.
Bake
Bake for 10-12 minutes, or until edges are just set and cookies are barely starting to brown. Let cool on the tray for 5 minutes, then transfer to a wire rack.