Pre-heat oven to Gas 4 (350°F/180°C). Put the brown sugar and butter into a saucepan and gently melt but do not let it boil. Remove from heat and stir in the porridge oats. Grease a china or aluminium flan dish, about 9–10 in diameter (23–25.5 cm). Put the mixture into the dish and spread evenly. Bake it in the top half of the oven for 15–20 minutes. Cool slightly. Stir the yoghurt, soured cream, sugar and lemon peel together and pour on top of the flapjack base. Put dish back in the oven for 8 minutes. Cool. Slice the strawberries in half and arrange them on top of the soured cream and yoghurt which will have gone smooth and slightly firm. Melt the redcurrant jelly gently and glaze the strawberries with it (I find it easiest using a pastry brush but you can spoon it over if you like). Once you have glazed it keep it in a cool place but not the fridge. You can make the first two layers the day before but do not put the fruit on top sooner than 2 to 3 hours before eating it. Serve with cream, and use a sharp knife to cut into the crisp flapjack base.