Preheat your oven to 350°F and lightly grease a 9-inch cast-iron skillet or a similar oven-safe dish.

In a separate bowl, combine the flour, baking powder, and sea salt, mixing well to incorporate.

In a large mixing bowl, beat the softened butter with brown and granulated sugars until creamy and fluffy, about 3 minutes.

Stir in the vanilla extract and egg, blending until smoothly combined.

Carefully add the dry mixture to the wet ingredients, stirring gently until just combined.

Fold in the dark chocolate chunks and walnuts, ensuring even distribution throughout the dough.

Spoon the cookie mixture into the prepared skillet, spreading it out evenly.

Bake in the oven for 20-25 minutes, watching for the edges to turn golden brown while the center remains gooey.

Allow to cool for a few minutes before serving. Top each slice with a scoop of vanilla ice cream.