In a medium bowl, stir together the flour, oats and 3/4 cup of brown sugar. Cut in the butter until the mixture is crumbly. Reserve 1 1/2 cups of this mixture and press the remaining mixture into the bottom of a 20x30cm pan.
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 crust. Empty the cranberry sauce into a small bowl and stir in the cornflour and brown sugar. Spoon over the cream cheese layer. Sprinkle the top with the reserved crust mixture.
Bake for 35 to 40 minutes in the preheated oven until top is golden. Let cool completely before cutting into bars. Store covered in the refrigerator.