For the jam: place all ingredients except for cornflour in a pan and bring to the boil with a decent splash of water until the frozen fruit is starting to break down. Taste and add more sweetener if needed. Mix about 1-2 tbsp of the jam with the cornflour in a separate bowl to make a paste, then pour back into the pan and simmer for 3-5 mins, stirring often, until the mixture is nice and thick. Repeat with more cornflour if it is not thick enough (it should look like jam - jelly to American readers). Allow to cool then keep in the fridge while you make the dough.

To make the dough, blitz the flour, oats and cornflour in a food processor for 30 secs or so, then add in the rest of the ingredients and blend until it becomes a ball of dough (add a splash of dairy or non-dairy milk, or a little extra flour if it looks too sticky or too dry - it should be like a fairly glossy dough but shouldn't stick to your fingers).

Wrap the dough in cling film and leave in the fridge for at least 15 mins, then roll out to a large rectangle about 1/2 cm (1/4") thick. Cut into 12 squares, then spread about 1-2 tbsp of the filling onto the centre of each square before folding the sides over the filling and pressing them together lightly.

Transfer each bar to a lined baking tray and preheat the oven to 180C/350F/gas 4 while you put them back in the fridge for at least another 15 mins.

Bake in the preheated oven for 20-25 mins, until slightly browned and firm. Allow to cool completely before serving. These will keep, individually wrapped, for about 1 week in the fridge.