Preheat the oven to 180C/350F. Line an 8 x 8-inch pan and pour your Biscoff spread into it and spread out in an even layer. Place the pan in the freezer to firm up while you prepare the other ingredients.
In a small bowl, add your flour, cocoa powder, baking powder, and salt, and mix well. Set aside. In a microwave safe bowl, add half the chocolate and microwave it until melted.
In a large mixing bowl, add the sugar and vegan butter and whisk until combined. Add the vanilla, flax eggs, and melted chocolate and whisk until combined. Gently fold through the dry ingredients, followed by the remaining chocolate.
Remove the pan from the freezer and remove the firm Biscoff spread from it. Transfer half the brownie batter into the lined pan. Add the thick layer of Biscoff, followed by the remaining brownie batter. Place the pan in the oven and bake for 40-45 minutes, or until a skewer comes out mostly clean.
Remove the brownies from the oven and let them cool completely, before slicing and serving.
* To make flax eggs, combine two tablespoons of ground flaxseed into a bowl and add 6 tablespoons of water or black coffee on top. Whisk together, and let the mixture sit for 10 minutes, for a gel to form. TO STORE: Brownies can be stored at room temperature in a sealed container. They will keep well for up to 1 week. TO FREEZE: Place brownies in a ziplock bag and store them in the freezer for up to 6 months.