In a medium bowl, stir together the flour, oats and 110g dark brown soft sugar. Rub in the butter until the mixture is crumbly. Reserve 200g of this mixture and press the remaining mixture into the bottom of a 20x30cm tin.
Bake for 15 minutes in the preheated oven.
Meanwhile, in a small bowl, beat cream cheese with sweetened condensed milk until light and fluffy. Stir in the lemon juice and spread the mixture evenly over the prepared base.
Empty the cranberry sauce into a small bowl and stir in the cornflour and dark brown soft sugar. Spoon over the cheese layer. Sprinkle the top with the reserved oat mixture.
Bake for 35 to 40 minutes in the preheated oven, until top is golden. Let cool completely before cutting into slices. Store covered in the fridge.