Preheat oven to 350. Grease a 13 x 9 pan. For the crust: beat the flour, butter, and brown sugar in a small mixing bowl until crumbly. Press into the pan and bake for 12-15 minutes or until lightly browned.
For the filling: beat the eggs, corn syrup, sugar, butter, and vanilla with a wire whisk. Stir in the chocolate chunks and pecan pieces. Pour over the baked crust. Bake for 25-30 minutes or until set. Cut into bars when cool.