Melt 1 ¼ cups butter in a saucepan over medium heat, stirring constantly. After 5–7 minutes, it will turn golden brown with nutty aromas and browned bits at the bottom. Remove from heat and pour into a heatproof bowl, scraping in all browned bits. Cool for 10 minutes, then refrigerate until solid (about 90 minutes). After 30 minutes, cover tightly.

Remove the solidified brown butter from the refrigerator and transfer it to a large bowl (or the bowl of a stand mixer). Using a handheld mixer or a stand mixer fitted with the paddle attachment, beat on high speed for 1–2 minutes until smooth and creamy. It may appear slightly grainy at first, but continue beating, and it will smooth out. If the butter is too firm to cream, let it sit at room temperature for 5–10 minutes. You can also microwave it for 5–8 seconds to soften it slightly, but be careful not to melt it—the butter should stay solid, just soft enough to mix easily.

Add 1 ¼ cups brown sugar and ¾ cup granulated sugar. Beat until well combined, about 2 minutes.

Mix in 2 eggs one at a time, then add 2 teaspoons of vanilla extract and mix until smooth.

Dissolve 1 teaspoon baking soda in 2 teaspoons water and add to the batter along with ½ tsp salt. Stir in 3 cups of flour and 2 teaspoons of corn starch. With the mixer running on low speed, slowly drizzle in 1 tablespoon of milk and mix until fully incorporated. The cookie dough will be thick and soft.

Fold in 1 ½ cups of chocolate chips until evenly distributed.

Cover and chill for 30–60 minutes.

Preheat oven to 350°F (175°C). Scoop dough onto baking sheets. Bake for 10–12 minutes, until edges are golden and centers are soft.

Sprinkle with flaky sea salt if desired. Cool on baking sheet for 5 minutes, then transfer to a wire rack.