Preheat oven to 350°. Beat butter, sugar, eggs, and vanilla together. Stir in flour, baking powder, and cinnamon. Mix well. Add in walnuts. Divide dough in ½. Shape into 2 long rolls approximately 1-½ inches in diameter. Place on greased baking sheet and flatten slightly. Bake 18-20 minutes, until firm. With sharp knife, cut diagonally into ¾ inch slice. Place cut side down on baking sheet. Bake 10 minutes longer or until lightly browned.