Place the butter in a microwave-safe bowl and microwave for about 10 seconds, just until melted.
Pour the melted butter into a food processor.
Add the molasses sugar and egg, then blitz briefly until the mixture becomes smooth and glossy.
Add the baking powder and a pinch of salt, then pulse once or twice to combine.
Fold in flour and mix gently until a soft cookie batter forms.
Line a small metal plate or pan with baking paper.
Spread half the batter onto the plate.
Add a ball of pistachio spread to the centre.
Cover with the remaining batter, gently spreading it so the pistachio filling is enclosed.
Place the plate into the air fryer and cook at 165°C for about 10 minutes. Time varies depending on your airfryer and your preference for done-ness.
Allow the cookie to rest for about 8-10 minutes before eating. This helps the cookie firm up slightly while keeping the centre molten.