A wonderful use of fresh maple syrup! When we served these at a party, they were gobbled up in no time.
Preheat the oven to 350 degrees F. Grease a 9-inch by 13-inch baking pan.
Make the crust by combining the 1-½ cups flour, ¼ cup brown sugar, and butter. Blend with a fork until the mixture has the consistency of cornmeal. Pat into the baking pan. Bake for 15 minutes.
Meanwhile, make the filling by combining the ⅔ cup brown sugar and the maple syrup in a saucepan and simmering for 5 minutes. Pour this over the beaten eggs, stirring constantly. Stir in the 2 tablespoons flour, salt, and vanilla. Pour over the partially baked crust. Sprinkle with the nuts.
Return the pan to the oven and bake for 20 to 25 minutes more. Cool completely before cutting into squares.