Preheat oven to 180 degrees C. Grease a 20x30cm pan.
Combine the butter, brown sugar, flour, bicarb soda, salt and rolled oats. Press 2 cups of the mixture into the bottom of the prepared pan. Spread the jam over the top and sprinkle with the remaining crumb mixture, gently pressing crumbs into jam.
Bake for 35 to 40 minutes. Allow to cool before cutting.