Pre-heat your air fryer, if required, to 190C (375F).
Get yourself a large mixing bowl.
Combine together the white sugar, plain flour and vanilla extract.
Wash the rhubarb and remove the ends. Cut into ½ inch thick pieces.
Add the rhubarb to your filling mixture.
Stir well.
Place into the lightly greased ramekins.
Combine together the flour and butter, til you have a crumble consistency.
Add the salt and brown sugar and mix well.
Place this over the top of your filling.
Air fry at 190C (375F) for 15 minutes.
Serve with lashings of custard and enjoy!