Brown the butter

• Cut the butter into cubes and place in a saucepan.
• Over medium heat, let the butter melt, then simmer, stirring frequently, until golden brown, about 10 minutes.
• Pour into a separate bowl and let cool for 15 minutes.

Mix the wet ingredients

• In a large bowl, mix together the cooled brown butter, brown sugar and granulated sugar.
• Mix in the egg, egg yolk and vanilla extract.

Add the dry ingredients

• Add the flour along with the baking powder and mix until just combined.

Fold in the chocolate and walnuts

• Fold in the milk chocolate chips, semi-sweet chocolate chips and chopped walnuts.

Portion and chill

• Using an ice cream scoop, scoop out 11 equal cookies onto a tray.
• Cover and refrigerate for a minimum of 1 hour, up to 48 hours.

Preheat the oven

• 10 minutes before baking, preheat the oven to 170 °C on the fan setting.

Bake the cookies

• Place the cookies on a baking tray lined with parchment paper, leaving space between them.
• Bake in the preheated oven for 12 minutes.

Serve

• Enjoy the cookies.