In a stand mixer fitted with a paddle attachment, combine the butter, sugar, golden syrup, baking soda, salt, and coconut extract (if using). Start mixing at a low speed to moisten the ingredients, then increase to medium speed. Beat until the mixture is light and fluffy, which should take about 5 minutes. Pause halfway to scrape down the bowl and paddle.

Sift the flour and cocoa powder together in a separate bowl. Gradually add the dry ingredients to the butter mixture, mixing on low speed. Once combined, knead the dough briefly by hand to form a cohesive mass.

Divide the dough into two portions, shaping each into a flat disc. You can proceed immediately or wrap the discs in plastic wrap and refrigerate for up to 1 week. Before rolling, allow chilled dough to soften at room temperature for about 30 minutes.

Preheat the oven to 350°F, positioning the rack in the middle. Dust a clean surface with cocoa powder.

Roll out one portion of the dough into a 7-inch square, about ¼ inch thick. Sprinkle cocoa powder over both sides of the dough and continue rolling until the thickness is reduced to about ⅛ inch. Optionally, use an embossed rolling pin for a decorative design.

Use a 1½-inch fluted cutter to stamp out rounds, and carefully transfer them to a parchment-lined baking sheet, leaving about ¼ inch of space between each. Use an offset spatula to lift the dough as needed, brushing away excess cocoa powder.

Re-roll any scraps, cutting more rounds until all the dough is used. Extra scraps can be baked and crumbled for other uses, such as garnishes.

Bake the wafers for approximately 15 minutes, or until they are dry and firm. Cool them completely on the baking sheet before handling.

Turn half of the cooled wafers upside down. Pipe or spoon about 1 tablespoon of the vanilla filling into the center of each inverted wafer.

Place another wafer on top of each filled cookie and gently twist to evenly distribute the filling. Let the cookies rest at room temperature for about 30 minutes to allow the filling to set.

Store the completed cookies in an airtight container at room temperature for up to 1 week, refrigerated for 1 month, or frozen for up to 3 months.