Preheat oven to 350 degrees F. Line a 9x13 pan with parchment paper or tinfoil so the paper comes over the edges of the pan, making it easier to remove the bars once cooled.
Combine the ingredients for the crust in a large bowl and use a pastry cutter to make a coarse and crumbly mixture. Alternatively you can place the ingredients into your food processor and pulse until mixture becomes crumbly.
Press the mixture into an even layer in the prepared 9x13 pan. Bake for 15 to 20 minutes or until a pale golden brown.
While the crust is baking combine the ingredients for the filling in a large bowl and whisk until smooth. Pour mixture over the crust and bake for an additional 30 to 35 minutes, or until the center is set.
Let bars cool completely and then lift out of the pan by holding the sides of the paper and lifting straight up. Cut into bars and dust with powdered sugar. Keep refrigerated. Enjoy!