Toast the milk powder: Set a dry skillet over medium-low heat. Add the milk powder and stir constantly until it turns golden and smells toasty, 3–5 minutes. Transfer to a bowl immediately so it doesn’t burn.

Brown the butter: In a saucepan, melt the butter over medium heat. Continue cooking, stirring, until the milk solids turn deep amber and smell nutty, 5–7 minutes. Scrape into a heatproof bowl, including the browned bits. Cool 10 minutes.

Combine dry ingredients: In a bowl, whisk flour, baking soda, and salt. Set aside.

Mix the sugars and butter: Add granulated sugar and brown sugar to the warm brown butter. Whisk or beat until glossy and combined, about 1 minute.

Add eggs and vanilla: Whisk in the eggs one at a time, then the vanilla, mixing until the batter looks smooth and slightly thick.

Stir in toasted milk powder: Sprinkle the toasted milk powder into the wet mixture and stir until evenly distributed.

Bring it together: Add the dry ingredients and fold just until a few streaks of flour remain. Fold in the chopped chocolate. Do not overmix.

Chill: Cover and chill the dough for at least 30 minutes and up to 24 hours. A short chill improves flavor and reduces spreading.

Prep to bake: Heat the oven to 350°F (175°C). Line baking sheets with parchment paper.

Scoop: Portion dough into 2-tablespoon mounds (about 40–45 g each). Space 2 inches apart. Top with a few extra chocolate pieces if you like.

Bake: Bake 10–12 minutes, until the edges are set and golden but centers still look slightly underdone. Tap the pan once on the rack to deflate for crinkles.

Finish: Sprinkle with flaky sea salt. Cool on the sheet 5 minutes, then transfer to a rack to finish setting.