Add butter to a saucepan over medium heat. Cook until golden brown and nutty, about 4–6 minutes.
Pour into a bowl and let cool 15 minutes so it thickens slightly. This replaces the chill step.
Whisk brown butter with brown sugar and granulated sugar until smooth and glossy.
Whisk in egg, egg yolk, and vanilla until fully combined.
In a separate bowl whisk together flour, cornstarch, baking soda, and salt. Stir into the wet ingredients until just combined.
Fold in chocolate chips. The dough should be soft but scoopable, not runny. If it feels too loose, add 1–2 tablespoons flour.
Scoop large dough balls (3 tablespoons each) onto a parchment-lined baking sheet. Keep them tall rather than flattening them.
Bake at 375°F for 10–12 minutes. The edges should be set while the centers remain soft and slightly underbaked.
Sprinkle with flaky sea salt and let rest 5 minutes before scooping. The centers stay soft and scoopable.