Stir together flour and baking soda. Beat peanut butter, margarine, brown sugar and vanilla in large bowl on medium speed until creamy. Beat in egg until light and fluffy. Gradually stir in flour mixture. Divide dough in half. Wrap and refrigerate at least 2 hours. Heat oven to 375 degrees. Lightly grease cookie sheet. Roll one half of dough 1/4 inch thick on well-floured surface. Cut with 4-inch gingerbread cutter. Repeat with remaining dough. Place 2 inches apart on cookie sheet. Bake 8 to 10 minutes or until edges are golden brown. Immediately remove from cookie sheet; cool completely. Decorate with colored frosting, colored sugar and assorted candies if desired. Makes about 2 dozen cookies.