Heat oven to
300F (150C). Grease an 8-inch (20.5-cm) square cake pan. Melt butter or
margarine in medium saucepan. Stir in brown sugar, vanilla, rolled oats
and nuts. Sift flour, baking powder and salt together into the mixture and
mix first with spoon then with fingers until blended. Turn into prepared
pan and press down evenly. Bake until set, about 25 minutes. Let cool in
pan 10 minutes then cut into squares. Finish cooling in pan.