Put the dried fruit, if using, in a small heatproof bowl and cover with hot water (unless it’s soft and plump already). Leave to sit while you get on with the dough.
Beat the butter with an electric whisk until soft, then add the sugars and salt, and continue beating for about three minutes, scraping down the sides of the bowl as you go, until the mixture is light and fluffy.
Beat the egg, yolk and vanilla extract into the mixture until well combined, then sift in the flour, oat flour and bicarb and fold into the dough until just mixed.
Drain the fruit well and pat dry, then stir it into the mix with the oats, oatmeal and, if you’re using them, the nuts.
Cover or wrap the dough and chill for at least an hour, and preferably a couple of days.
Line two baking trays with greaseproof paper and heat the oven to 200C (180C fan)/ 390F/gas 6.
Use your hands to pinch off 50g pieces of dough, roll these into balls and arrange well spaced out on the baking trays.
Bake for about 18 minutes, until golden brown and firm around the edges, then remove, sprinkle with a little coarse salt and leave to cool on the trays.
