Preheat the oven to 385 F. Line two trays with parchment paper.
Add the butter, fine granulated sugar, and brown sugar to a mixing bowl. Cream the butter and sugar using electric beaters until the mixture is pale fluffy.
Add one egg and mix it into the butter and sugar mixture until well combined. Add the second egg and the vanilla, and mix again.
In a separate bowl, mix the flour, baking soda, baking powder, and fine salt together.
Add the flour mixture into the butter mixture and mix until just combined.
Fold in walnuts and chocolate into the batter.
Divide the dough into 12 pieces and roll into large balls.
Place four balls of dough onto each lined tray. If using the flaky salt, sprinkle onto the dough balls. Cook for 12-15 minutes or until golden and crisp.
Remove the cookies from the oven and allow to cool for five minutes.