Line a 20 x 20cm square pan with baking parchment so that it reaches up the sides as well as covering the base.
Measure the dairy free spread, maple syrup and 300g (reserve 40g of peanut butter for later) of the peanut butter into a small saucepan (reserving the rest for later . Cook, stirring regularly, over a gentle heat until the mixture is liquid but not boiling.
Pulse the oats and popcorn in a food processor a few times to break everything down a little. Pour in the liquid peanut butter mixture and pulse again a couple of times to combine.
Tip everything from the food processor into the prepared pan and press down and even the surface with a spatula. Cover and place in the fridge to chill for 20 minutes.
Meanwhile, melt the chocolate in a heatproof bowl suspended over a pan of barely simmering water making sure the base of the bowl doesn’t touch the surface of the water. When the chocolate has melted, pour it over the peanut butter popcorn mixture.
Working quickly, heat the remaining peanut butter in a pan until liquid but not boiling. Use a teaspoon to dot liquid peanut butter all over the surface of the chocolate, then use a knife to create an attractive swirl pattern over the top. Cover and return to the fridge for at least 2 hours before cutting into 9 squares.