Preheat oven to 350℉ (180℃). Line 2 baking trays with parchment paper or silpat and set aside.
In one of the baking trays, measure out 1 tbsp of the cookie butter spread and plop it onto the tray. Repeat until you have a total of 14 tbsp. Cover with cling wrap and place in the freezer to solidify.
In a small bowl, combine the flaxseed and 3 tbsps of water to create a flax egg. Leave for around 5 minutes to thicken.
In a large bowl, sift together the flour, baking soda, salt and spices.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugars until light and fluffy, around 2-3 minutes. Add in the flax egg, maple syrup and vanilla. Beat until smooth and silky.
Add half of the flour mixture to the batter and mix on low speed until just incorporated. Add in the remaining half and combine until there are no more flour streaks.
While the batter is mixing, make the cinnamon sugar by combing the sanding sugar and cinnamon.
Using a 2 oz ice cream scooper (70g of cookie dough), create a dough ball and use your thumb to create a dent in the center. Place a frozen tbsp of biscoff in the middle then fold the dough to seal the biscoff inside. Dip half of the ball* in cinnamon sugar then place on the tray, sugar side up. Repeat this process then bake the cookies for 13-15 minutes or until the edges have crisped up but the center still looks soft. It will firm up as it cools on the tray.
After 10 minutes, transfer to a wire rack to cool completely or serve warm with vanilla ice cream. Enjoy!