Preheat oven to 350 and line an 8x8 baking dish with parchment. In a large bowl, mix melted butter, brown sugar, flour, baking powder, salt, and oats until crumbly. Press half of the crumb mixture evenly into the bottom of the prepared baking dish. In a separate bowl, stir the raspberry preserves until smooth, then spread evenly over the crust. Sprinkle the remaining crumb mixture over the top. Bake for 25 to 30 minutes until the top is golden brown. Let cool completely before cutting into bars.
