Preheat the oven to 200 degrees C. Grease a 20x30cm pan.
In a large bowl, cream together the butter and brown sugar until smooth. Combine the oats, flour, salt and baking powder; stir into the creamed mixture. Press half of the mixture into the bottom of the prepared pan. Spread the preserves over the crust. Crumble the remaining crust mixture over the raspberry layer.
Bake for 20 to 25 minutes in the preheated oven, or until light brown. Cool completely before cutting into bars.