Preheat oven to 350°F (175°C) with the rack in the middle position and line an 8×8 inch (20×20cm) light-colored aluminum baking pan with parchment paper leaving a 2-inch overhang on all four sides.

Whisk together 150g all-purpose flour, 60g sifted powdered sugar, and 1.5g fine sea salt in a large bowl until evenly combined, then pour in 115g melted cooled unsalted butter and stir with a silicone spatula until the mixture comes together into a soft, sandy dough.

Transfer the dough to the lined pan and press into an even, compact layer using your fingers then the flat bottom of a measuring cup or straight-sided glass, working from the center outward and reinforcing the corners.

Bake the shortbread base for 18–20 minutes until the edges are pale golden and the center looks matte and dry, then remove from the oven and set on a wire rack — do not remove from the pan.

While the base cools for 10 minutes, make the toffee: place 85g room-temperature cubed unsalted butter and 165g packed light brown sugar in a medium heavy-bottomed saucepan over medium heat and stir constantly with a silicone spatula until the butter melts and the mixture is smooth and glossy — about 3–4 minutes.

Clip a candy thermometer to the side of the pan and continue cooking and stirring over medium heat until the mixture reaches exactly 248°F (120°C) — firm ball stage — watching the thermometer closely as the toffee deepens from pale gold to rich amber.

Remove the pan from the heat immediately at 248°F and pour in 60g heavy cream in a slow steady stream while stirring constantly — the mixture will bubble vigorously, which is normal — then stir in 2g fine sea salt and 2g pure vanilla extract until smooth.

Pour the hot toffee immediately over the par-baked shortbread base and spread quickly and evenly to all four edges with an offset spatula, then allow the toffee layer to cool and set at room temperature for 15 minutes.

Place 170g semi-sweet chocolate chips and 85g heavy cream in a small microwave-safe bowl and microwave on 50% power in 30-second intervals, stirring between each, until mostly melted — about 60–90 seconds total — then stir slowly from the center outward until the ganache is completely smooth and glossy.

Allow the ganache to cool at room temperature for 3–5 minutes until it falls in a slow thick ribbon from the spatula, then pour it over the set toffee layer and spread with an offset spatula in smooth even strokes to all four edges, tapping the pan gently on the counter twice to level.

Immediately scatter 120g sweetened shredded coconut evenly across the wet ganache surface and press very lightly with your fingers so it adheres — the coconut should sit proud on the surface, not be pushed into the ganache layer below.

Bake for 14–17 minutes, rotating the pan 180 degrees at the 8-minute mark, until the coconut tips are deep copper and the base of the coconut layer is golden — watch closely in the final 3 minutes as the coconut can go from correct to burnt quickly.

Remove from the oven and immediately scatter 1.5g flaked sea salt evenly across the coconut surface, pressing each flake very lightly with a fingertip to make contact with the coconut beneath.

Cool on a wire rack at room temperature for 45 minutes, then transfer to the refrigerator and chill for a minimum of 2 hours — 3 hours is better, overnight is best — until all layers are fully cold and set.

After chilling, scatter 10g large white coconut flakes across the surface as the final garnish, then lift the slab from the pan using the parchment overhang, set on a cutting board, score the surface along cut lines, and slice into 16 even 2×2 inch (5×5cm) squares with a cold sharp knife wiped clean between every cut.