Preheat oven to 350°.
In bowl beat 3 cups cracker crumbs, butter, sugar and flour until well blended. Press firmly into 9x13" pan. Bake until golden brown, 10-15 minutes.
While crust is baking, whisk together brown sugar, eggs until blended. Whisk in 2/3 cup graham crackers, vanilla, salt, baking powder until well blended. Stir in pecans.
Spread mixture over baked crust. Return to oven and bake until filling is golden brown on top and jiggles sightly, approximately 20-25 minutes.
Remove from oven. Cool completely.
Sprinkle a light coating of powdered sugar over bars, is desired. Bars can be made 1 day in advance. Wrap in plastic. Keep at room temperature.