First up, preheat your oven to 200°C/180°C/Gas mark 6 and line a 8” square baking tin with baking parchment.
Next up, cream together the butter and sugars in a large bowl until pale and creamy. Pop in Vanilla and the eggs and mix until smooth.
Stir in the flour and Baking Powder and mix until a dough begins to form. Pour in the nuts and mix through until all combined.
Pop your cookie dough into your prepared tin and press down into the tin to create an even layer. Bake for 20-25 minutes. Leave to cool in the tin for 20 minutes, then pop on to a wire rack to cool completely.
To decorate, break your White Chocolate into pieces and pop into a microwavable bowl, melt in the microwave in 20 second bursts stirring between each burst until melted and smooth. Repeat this for the Milk Chocolate.
Cut the cookie into pieces and decorate it as you like with the melted Chocolate and Sprinkles. Now your delicious cookie tray bake is ready to eat!