Line a 13x9 baking pan with aluminum foil. Lightly coat with cooking oil. Set aside.
Place flour, brown sugar, confectioner's sugar and butter in a food processor. Plus for one minute or until dough comes together. If dough isn't coming together after one minute, slowly add up to 2 tablespoons cold water, stop when the dough forms a ball.
Press dough evenly into prepared baking pan. Cover bottom and 1/2 inch up the sides.
Bake in a 350 degree preheated oven for 25 minutes or until crust is brown. Remove from oven and fill with filling while crust is still warm.
Whisk together all ingredients in a large bowl until flour is well incorporated into the liquid.
Pour filling onto warm crust.
Bake at 350 degrees for 30 minutes or until the filling is set.
Cool to room temperature.
Dust with confectioners sugar.