Prepare your flax egg by combining 1 tbsp of ground flax with 3 tbsp of water. Mix + let it sit for 10 minutes.
Preheat the oven to 350 degrees F and grease a baking tray.
Using an electric mixer (hand or stand0 cream (mix) together the softened butter, brown sugar and regular sugar until combined. It will look gritty.
Add in flax egg, vanilla extract. biscoff and plant based milk + mix. The dough will look very loose.
Slowly mix in the baking soda, baking powder and flour. Mix until combined. The dough will look soft, yet moldable. It should not stick to your hands.
Scoop 1 tbsp of the dough into your hand and roll it into a ball then place it onto the baking tray.
Continue until all dough is used. Space each cookie dough ball approx. 3-4 inches apart. You likely will need to use multiple trays.
Place baking tray into the oven on the TOP rack. You will likely have to bake in batches.
Bake for 13-15 minutes. The cookies will look soft, but they will continue to cook while cooling.
Allow to cool for 10 minutes.
Optional: After 5 minutes of cooling, place backside of a spoon gently onto the cookie to create a small cavity. Fill cavity with approx. ¼ tsp of biscoff. The biscoff will melt while the cookies cool.