Place racks in the middle rack of the r convenient or toaster oven and preheat to 375°.
Line a baking sheet with parchment.
In a 2 cup measuring cup whisk together the flour, baking powder, baking soda, and kosher salt and set aside.
In a large bowl, cream the butter, brown sugar, confectioners sugar, and granulated sugar. in a separate bowl using a hand mixer on medium speed to until smooth and fluffy, about 3-4 minutes.
Add the egg yolk and vanilla and beat until light and fluffy, about 5 minutes.
Reduce the hand mixer speed to low and gradually add the dry ingredients until just blended.
With a wooden spoon fold in the chocolate.
Use a small cookie scoop to place cookie dough onto the parchment-lined baking sheet.
Sprinkle the cookies with sea salt.
Bake cookies on middle rack rotating baking sheet halfway through baking, about 5 minutes. Continue baking for an additional 5-7 minutes or until just golden brown around the edges.
Let cool slightly then transfer to wire racks to cool completely. Cookies will firm up as they cool.