Chop the dark chocolate and add in the butter. Melt both in microwave or stovetop using double boiler method.
To this, add the Speculoos butter, Vanilla extract, Condensed milk and Milk.
In a separate bowl, measure flour, cocoa powder, baking powder and salt. Sift them.
Add the dry ingredients to the wet ingredients gradually and combine to get a thick batter.
Transfer the batter to an 8x8 square baking dish and top it with few Biscoff Cookies. You may also drizzle some Speculoos over the top optionally.
Bake for 40 minutes at 180°C
Let cool for few hours before slicing. You can make this a day ahead and slice before serving.