Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4, and grease and line a 12" x 9" traybake tin
To make the flax eggs: 2 tbsp linseeds/flaxseeds (ideally ready ground or you can grind them up in a food processor, with a pestle and mortar or spice grinder) soaked in 4 tbsp water for at least 10 minutes in the fridge.
In a bowl mix together the plain flour, caster sugar, cocoa powder, baking powder and salt
In another bowl or a large jug, whisk together the almond milk, flax eggs, vegetable oil and vanilla extract, then add it to the dry ingredients and mix together
Pour the batter into the lined baking tray, then add the broken oreo pieces all over the top
Bake for 30-35 minutes or until a skewer comes out clean, leave to cool completely
Once cool, melt the dark chocolate and drizzle it all over the brownies, allow the chocolate to set (if you can!), then cut into squares then serve
Store in an airtight container in a cool place and eat within 4 days