Whisk together the flour, salt and baking soda in a bowl and set aside.
Brown 1/2 cup butter in a saucepan, swirling, until butter foams and starts to turn brown and smells nutty. Transfer butter to a liquid measuring cup and see how much water content you lost. You want to have 1/2 cup of butter, so stir in the remaining 1-2 tablespoons of butter if you need it – the butter you add in should melt slowly and not foam up.
When the butter is melted and slightly cool, whisk in both sugars until incorporated with no lumps. Whisk in the egg until smooth and glossy. Stir in the vanilla and use a rubber spatula to fold in the dry ingredients until no dry spots remain. Fold in the chocolate.
Use a 1.5 tablespoon cookie scoop and scoop out two balls of dough, so that each cookie is 3 tablespoons large. Smoosh the two balls on top of each other – they should kind of look like a log and you should get about 14-16 cookies depending on how big your chocolate chunks are. Place the logs on a parchment paper lined cookie sheet, cover with plastic wrap and let chill in the fridge for 15-30 minutes, or as long as it takes for your oven to heat up.
Arrange the racks in the upper and lower thirds of the oven and heat to 375°F.Space out the cookie logs (standing tall) on parchment paper lined rimmed baking sheets, leaving plenty of space in between. Bake, rotating and moving trays halfway if browning unevenly. Bake until golden brown and firm around the edges, 10-12 minutes.
Remove from the oven and bang the pan down against the counter top (this helps create a couple of ripples like you see on Instagram). Sprinkle with flaky sea salt, let cool on the baking sheets and enjoy!