• Preheat your oven to 180°C (or 160°C if you're using fan setting) and line an 8x10-inch tin with baking paper.
• Add the butter to a bowl with the caster sugar and brown sugar. Mix well.
• Stir in the egg, peppermint extract and vanilla extract. Mix well until smooth.
• Add all of the self-raising flour and cocoa powder. Mix well and when it starts to come together, use your hands to press it into a ball.
• Press the mint chocolate chunks and white chocolate chips into the dough.
• Take ¾ of the cookie dough and press it into the bottom of your lined tin. Set the rest aside to use as the topping later.

Fudge layer:

• Break the white chocolate into pieces and place it into a saucepan with the condensed milk and peppermint extract. Place over low heat on the stove and stir gently until the chocolate has fully melted.
• Pour the fudge mixture over the cookie dough in the tin and spread it out evenly. Work quickly as it'll start setting as soon as you remove it from the heat.
• Divide the remaining cookie dough into 4 pieces and use your hands to flatten each piece as much as you can. Place the pieces over the fudge then use a toothpick to swirl them together.
• Top with red M&Ms and white chocolate chips.
• Bake for 22-25 minutes, then sprinkle crushed candy canes on top as soon as it comes out of the oven.
• Leave it in the tin to cool completely then pop it in the fridge for 2-3 hours to set.
• Once set, remove the cookie from the tin, cut it into slices and enjoy!