Preheat the oven to 350°F / 175°C. Line a baking sheet with parchment paper or with a silicone mat.
In a medium sized microwave safe bowl, melt the butter in 20 second intervals, until it's *just* melted. The hotter the butter, the more the cookies will spread.
Add the light brown sugar to the butter and whisk until combined.
Add in the egg yolk and vanilla, whisking until thoroughly combined.
Add in the flour, baking soda, baking powder and salt. Lightly fold together using a rubber spatula until the flour is almost completely combined. Add in the chocolate (save some for topping the cookies if desired), and fold until no flour streaks remain.
Use a 3 tbsp. cookie scoop to dish out the cookies and evenly space them out on the baking sheet. Top with extra chocolate if desired. Bake for 8-10 minutes, or until the edges are golden and the middles of the cookies are almost completely set.
Immediately after taking the cookies out of the oven, you can take a bowl that is slightly larger than the cookies and swirl it around over the cookies to make them a little more uniform and circular. Serve and enjoy!