Prepare your tray. Line a large baking tray with parchment paper. You want the paper to be snug against the tray so the cookies don't slide around later. The surface should feel smooth and be ready for the warm mixture.

Combine the wet base. In a medium saucepan, place the caster sugar, milk, unsalted butter, and golden syrup. Set the pan over a medium heat. Stir occasionally with a wooden spoon until the butter has fully melted. You will see the mixture become a uniform, pale yellow liquid with tiny bubbles forming around the edges. This takes about 3-4 minutes.

Boil the mixture. Once the butter is melted, increase the heat to medium-high and bring the mixture to a full, rolling boil. Let it boil for exactly 1 minute without stirring. You will hear a gentle bubbling sound and see the mixture rise slightly in the pan. The colour will deepen to a light amber and the texture will become syrupy. Do not skip this step, as it sets the cookies.

Remove from heat and add peanut butter. Take the pan off the heat immediately. Add the peanut butter and vanilla extract. Stir vigorously until the peanut butter is fully incorporated. The mixture will look glossy, thick, and smell deeply of toasted nuts. It should be smooth and free of streaks.

Fold in the dry ingredients. Add the rolled oats, desiccated coconut (if using), and salt. If you are making the chocolate version, add the cocoa powder now. Stir with a firm hand until every oat is coated. The mixture will look matte and feel quite stiff. It should hold together when pressed between your fingers.

Shape the cookies quickly. Working swiftly while the mixture is still warm, use a tablespoon or a small cookie scoop to drop heaped spoonfuls onto the prepared tray. Leave about 2cm space between each one. Press each mound down gently with the back of the spoon to form a thick disc. The edges should be slightly craggy, and the surface should look slightly moist.

Chill to set. Place the tray in the refrigerator for at least 30 minutes. The cookies will firm up as they cool. They should be firm to the touch and hold their shape when lifted. If they are still soft, give them another 10 minutes. Once set, they are ready to serve.