With the rack in the middle position, preheat the oven to 200°C (400°F). Line 2 baking sheets with parchment paper.
In a bowl, combine the flour, baking soda and salt. Set aside.
In another bowl, cream the butter and brown sugar with an electric mixer. Add the egg and beat until smooth and creamy. Using a wooden spoon, stir in the dry ingredients, nuts and chocolate.
With floured hands, shape dough into balls, about 30 ml (2 tablespoons) each. Arrange 8 balls on each baking sheet. Bake one sheet at a time until the cookies start to brown lightly around the edges, about 7 minutes. The cookies will be very soft in the centre.