Start by measuring out all of the ingredients before combining. Preheat the oven 170℃/338℉. Line a 23cmx33cm baking tin with baking paper (over lapping the tin'/s edges). Spray with baking spray to ensure a smooth release.
Add butter to a small saucepan and bring to a medium heat. Continue stirring the melted butter until the milk solids start turning light brown in color. Immediately turn off the heat and allow to cooldown. Note: the browned butter doesn't need to be fully cooled for you to continue with the below recipe
To a large mixing bowl, add the browned butter, brown sugar, egg, golden syrup and whisk mix until well combined, about 1 minute. Add milk an mix until well combined.
Bring a large saucepan to a medium heat and toast the desiccated coconut until golden brown. Note: the coconut browns very fast so stir continuously.
To the wet ingredients, add oats, toasted coconut, flour, baking powder, cinnamon and salt. Mix using a wooden spoon or sturdy spatula until well combined with no ingredient pockets left. Note: feel free to add the dry ingredients to a large mixing bowl and pre mix before adding to the wet ingredients.
Press the batter into the the prepared baking tin and even out the surface. Using a straight edged knife mark 8 rusks on the width and 4 rusks on the length. Pre slice the batter, yielding 32 rusks. Bake for 50-60 minutes.
Remove from the baked sponge from the oven and allow to cool slightly. Using a serrated knife, slice the rusks again, allowing for a smooth release.
Drying: Preheat the oven to 90℃/194℉. Lay the sectioned sponge out onto a baking tray that's been lined with a rack, ensuring the tray isn't overcrowded. Place in the oven, with the door slightly ajar, using a cloth or wooden spoon, and dry for 6 hours or until fully dried (overnight can also be an option). Note: the rusks must be fully dried otherwise they'll slowly start to soften and stale.