Preheat the oven

• Preheat the oven to 180 °C.
• Line a baking sheet with parchment paper.

Mix the dry ingredients

• Whisk together the flour, baking powder, baking soda and cornstarch in a medium bowl.
• Set aside.

Cream the butter and sugars

• In a large bowl, cream the brown sugar, granulated sugar and butter with an electric mixer.
• Mix until light and fluffy.

Beat in the eggs and vanilla

• Beat in the eggs one at a time.
• Add the vanilla extract and beat until the batter turns pale and the sugar is well incorporated.

Combine with the dry ingredients

• Gradually mix in the flour mixture until just combined.
• Be careful not to overmix.

Add the chocolate and walnuts

• Stir in the chocolate chips and chopped walnuts.

Shape the cookies

• Scoop tablespoon-sized balls of dough onto the prepared baking sheet, leaving about 10 cm between each cookie.
• Top with extra chocolate chips and walnuts.

Bake

• Bake until the edges are lightly golden brown.

Cool

• Let the cookies cool on the baking sheet for 5 minutes.
• Transfer to a wire rack to cool completely.