Brown the butter by melting it in a saucepan over medium heat until it turns foamy and browned. Remove from heat and let it cool to room temperature.
Preheat the oven to 350°F and line two baking sheets with parchment paper.
In a medium bowl, whisk together flour, baking powder, baking soda, cornstarch, and salt. Set aside.
In a large bowl, whisk together cooled brown butter, brown sugar, and white sugar until combined and creamy.
Add egg yolks, vanilla extract, and heavy cream to the butter mixture, whisking until pale and smooth.
Fold in the dry ingredients until just combined, then gently fold in the chopped chocolate.
Use a large cookie scoop to portion out the dough onto the prepared baking sheets, leaving 2 inches of space between each cookie.
Bake for 10 minutes until lightly golden brown, then use a circular cookie cutter to shape the cookies while they’re still warm.
Let the cookies cool on the baking sheet for five minutes, then transfer to a wire rack to cool completely. Sprinkle with flaky sea salt before serving.