I followed Stella Parks's recipe. She explained that the distinct flavor of Biscoff comes from caramelized sugar (regular brown sugar here is made with molasses) so I even made my toasted sugar. It's a bit time consuming but the homemade biscoff tastes like the real thing. So pleased, except that my cookies spread so much during my first try. Will shape the dough into a log and slice next time.
Homemade Biscoff by Stella Parks
Toasted Sugar, adapted from Stella Parks
Put 500 g sugar in a metal container (a 26-cm frying pan works for me). Toast the sugar at 160C for 30 minutes. Remove from the oven and stir thoroughly. Put the sugar back to the oven and remove/stir again after another 30 minutes. Do it two more times so that your sugar is toasted for a total of 2 hours. By now the sugar will look like wet sand and golden at this stage. Remove from the oven and keep stirring to help it cool. I find my sugar has the tendency to clump if I don't stir for 10 minutes after it's removed from the oven.
Cool down the sugar completely before bottling.
Biscoff cookie dough
150 g light brown candi sugar, such as Brewer's Best, or deeply toasted sugar (see above)
85 g unsalted butter, soft but cool, about 70°F
3/4 teaspoon baking soda (I used 1/2 tsp, may use less next time)
3/4 teaspoon ceylon cinnamon
1/2 teaspoon kinako (roasted soybean flour; 1g), such as Shirakiku, optional
1/4 teaspoon ground or freshly grated nutmeg
Shy 1/8 teaspoon (0.35g) Diamond Crystal kosher salt
Shy 1/8 teaspoon ground cloves
1/16 teaspoon ground cardamom
1/16 teaspoon ground anise
1 tablespoon tap water (15g)
155 g all-purpose flour (about 1 1/4 cups)
Adjust oven rack to lower middle position, and preheat to 350°F. In the bowl of a stand mixer fitted with a paddle attachment, combine candi or toasted sugar with butter, baking soda, cinnamon, kinako, nutmeg, salt, cloves, cardamom, and anise. Cream on medium speed until fluffy, soft, and pale, about 10 minutes, pausing to scrape the bowl and paddle as needed if the sugar seems dense and compacted at the bottom of the bowl.
While creaming on medium speed, slowly splash in the water a little at a time. Once it disappears into the fluffy butter/sugar mix, reduce speed to low and add the flour all at once. Continue mixing until the dough begins to gather around the paddle.
Turn the dough onto a clean surface, and knead gently to form a ball. Pat into a rectangular shape, then dust with flour, above and below. Roll to a thickness of 3/16-inch (5mm), using a ruler for guidance. Slide an offset spatula beneath the dough to loosen, and brush away the excess flour.
With a fluted pastry wheel, cut the dough into 3/4-inch strips, then cut crossways to form 2-inch rectangles. With the offset spatula, transfer the cutouts and scraps to a parchment-lined half sheet pan, leaving an inch between each piece to account for spread.
Bake until cookies are golden brown, about 16 minutes (mine was done at 8-9 minutes), rotating the pan halfway through if needed to ensure even browning. Cool to room temperature directly on the baking sheet; the cookies will not crisp until fully cool. Enjoy with coffee, and store leftovers in an airtight container up to 1 month at room temperature; the scraps can be ground to use for crumbs and frozen in an airtight container for up to 3 months.