Add butter to a saucepan over medium heat.

Swirl and stir frequently until the butter foams, turns golden, and smells nutty (about 3–5 minutes).

Remove from heat and pour into a bowl to cool slightly before using.

Line baking sheets with parchment paper.

In a small bowl, whisk flour, baking powder, baking soda, and salt.

In a separate bowl, beat the browned butter, brown sugar, and granulated sugar until smooth.

Add eggs and vanilla extract. Mix until well combined.

Gradually add dry ingredients and stir until a thick dough forms.

Scoop dough using a large cookie scoop (¼ cup size) and roll into balls.

Chill for 30 minutes to help cookies bake thick and chewy.

Preheat oven to 350°F (175°C).

Arrange 6 cookies per tray and bake for 12–14 minutes, until edges are set and centers are slightly soft.

Let cookies rest on the baking sheet for 5 minutes before moving to a wire rack.

Microwave Nutella for 15–20 seconds until smooth.

Transfer to a piping or zip-top bag and drizzle over cooled cookies.

Sprinkle lightly with flaky sea salt and let set before serving.