Preheat oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using a handheld mixer, beat the butter and granulated sugar together for 1-2 minutes or until well combined. Mix in the egg, egg yolk, and vanilla extract until fully combined, stopping to scrape down the sides of the bowl as needed.
In a separate mixing bowl, whisk together the flour, baking powder and salt. Add half of the dry ingredients to the mixing bowl with the wet ingredients and mix until just combined, then add the rest of the dry ingredients and continue mixing until fully combined.
Using a 1.5 tablespoon cookie scoop, scoop balls of cookie dough onto the prepared baking sheets, making sure to leave a little room between each one. Roll into balls and gently press down to slightly flatten the cookie dough.
Bake in separate batches at 350°F (177°C) for 11-13 minutes or until the tops of the cookies are set and the edges are lightly golden brown.
Remove from the oven and cool on the baking sheet for 5-10 minutes, then carefully remove the cookies and transfer to a wire rack to cool completely.