Homemade Oreo Cookies

Ingredients

• For the chocolate wafers:
• 4 ounces unsalted butter, creamy and soft, about 68°F
• 3 1/2 ounces sugar
• 2 ounces golden syrup, such as Lyle's
• 1/2 teaspoon baking soda
• 1/4 teaspoon Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 1/4 teaspoon coconut extract, optional
• 5 3/4 ounces bleached all-purpose flour, such as Gold Medal
• 1 1/4 ounces Dutch-process cocoa powder, such as Cacao Barry Extra Brute, plus more for dusting
• For the filling:
• 6 ounces unsalted butter
• 1 teaspoon vanilla extract
• 1/8 teaspoon Diamond Crystal kosher salt
• 8 1/2 ounces powdered sugar

Directions

1. Make the wafer dough first. Put the butter, sugar, golden syrup, baking soda, salt, and coconut extract, if you’re using it, into the bowl of a stand mixer with the paddle in place. Start on low just until everything is dampened, then turn the mixer to medium and let it whip until the mixture looks pale and airy, about 5 minutes; stop around the middle to scrape down the bowl and paddle.
2. Sift the flour with the cocoa. If you’re measuring by volume, spoon the dry ingredients into the cups, sweep them level with a knife, and then sift. With the mixer on low, add the flour-cocoa blend gradually to the butter mixture. It may look sandy and too dry at the beginning; keep going until it comes together into a smooth dough. Press and turn it against the inside of the bowl until it gathers into a neat ball, then split it in half and pat each piece into a disk. You can work with it now, or wrap it in plastic and chill it for up to 1 week; after chilling, leave it at room temperature for 30 minutes, then knead it on an unfloured counter until it feels supple and smooth.
3. Move an oven rack to the center and heat the oven to 350 degrees F (180 degrees C). Dust the work surface with cocoa and roll one piece of dough to a 7-inch square. Cocoa both faces of the dough, roll it to 1/4 inch thick, add another generous dusting of cocoa, and keep rolling until it reaches 1/8 inch; if you prefer, use an embossed rolling pin to bring the dough to 1/8 inch. Run an offset spatula underneath to free it from the counter, sweep off extra cocoa, and cut out 1 1/2–inch circles.
4. Set the cutouts on a parchment-lined aluminum baking sheet with 1/4 inch of space between them. Pull the trimmings together, knead them briefly, roll again, and cut more wafers the same way; do the same with the rest of the dough. Leftover bits can be thrown away, or you can bake them and turn them into crumbs. Bake until the wafers feel set and dry, about 15 minutes, then let them cool fully on the baking sheet. Fill them right away, or seal them in an airtight container and hold them at room temperature for up to 1 week.
5. Before you start the filling, turn half of the chocolate wafers over so their flat sides are ready; once the filling is mixed, it starts to firm up fast.
6. Use a 2-quart stainless steel saucier to melt the butter completely over medium-low heat. Keep it at a simmer, stirring with a heat-safe spatula while it crackles and spits; if brown flecks begin showing up near the sides, lower the heat. Stir and cook until the butter quiets down, then pour it through a strainer into the stand mixer bowl with the paddle attached.
7. Add the vanilla and salt, then the powdered sugar. Begin on low so the sugar can moisten, then beat on medium until the filling is soft and creamy, about 5 minutes. Spoon it into a sturdy pastry bag with a 1/2-inch tip and use it right away; this is not a make-ahead filling.
8. Pipe one generous mound of filling onto the middle of each wafer you turned over, using just shy of 1 tablespoon, or a little more than 1/4 ounce. Cap them with the remaining wafers, place the sandwiches in an airtight container, and let them sit at room temperature until the centers are set, about 30 minutes. For keeping them, use room temperature for up to 1 week, the fridge for up to a month, or the freezer for 3 months; bring them back to room temperature before serving.