Preheat the oven to 180°C, fan 160°C, gas 4. Line a 36 x 24 cm baking tray with baking parchment, allowing it to extend up the sides of the tray to form a 5cm collar.
Using an electric hand mixer, whisk together the butter and sugar. Add the eggs, whisking in one at a time, and the vanilla extract. Add the flour, baking powder and salt, and mix to combine. Stir in the nuts, coconut and chocolate.
Spread the mixture out in the tray as evenly as possible. Bake for 10 minutes, then rotate 180 degrees and continue to bake for another 10 minutes. Be careful not to over-bake.
Leave in the tray to cool completely, then chill in the fridge overnight. Once completely cold, cut into bars or squares to serve. They will have a lovely crunchy, slightly chewy texture.