Melt the butter gently over low heat. Remove from the heat and let cool until just warm to the touch.

In a large bowl, whisk together the brown sugar and granulated sugar. Pour in the melted butter and whisk until smooth and glossy.

Whisk in the egg and egg yolk until fully emulsified. Add the vanilla and rosewater and whisk until combined.

In a separate bowl, whisk together the flour, baking soda, baking powder, and salt. Add to the wet ingredients and fold just until no dry streaks remain.

Fold in the walnuts and chopped chocolate.

Scoop 2-tablespoon portions (about 60-65 g each) onto a parchment-lined baking sheet. Chill for 30–60 minutes, or up to 24 hours.

Preheat the oven to 350°F (180°C). Bake for 11–13 minutes, until the edges are set and lightly golden and the centers still look soft.

Cool on the tray for 5 minutes, then transfer to a rack to cool completely.