Preheat oven to 350°. In medium bowl, cream butter and sugar until fluffy. Stir in oats and vanilla. Sift flour and cardamom into small bowl. Add dry ingredients to creamed mixture; stir until soft dough forms. Press into greased 8-inch round shortbread mold or 9-inch round cake pan. Bake 25 to 30 minutes or until lightly browned. Cool in pan 10 minutes; loosen edges with knife. Invert onto cutting board. If necessary, tap edge of pan on cutting board. Cut warm shortbread into wedges. Cool completely. Store in airtight container. Makes 6 to 8 servings.
Bake in a shortbread mold for a lovely embossed effect.