1Heat oven to 350°F. Grease 13x9-inch pan. In small saucepan, combine raisins and water; bring to a boil. Drain; set aside.
2In large bowl, combine 1 cup brown sugar and margarine; beat until light and fluffy. Add flour, oats and baking soda; mix at low speed until crumbly. Press half of mixture in bottom of greased pan to form base. Bake at 350°F. for 8 minutes.
3In medium saucepan, combine sugar, 1/2 cup brown sugar and cornstarch. Stir in sour cream and egg yolks. Cook over medium heat until mixture thickens, stirring constantly. DO NOT BOIL. Stir in raisins, vanilla and rum extract. Pour evenly over base. Sprinkle remaining crumb mixture over filling.
4Bake at 350°F. for an additional 30 to 40 minutes or until light golden brown. Cool 1 hour or until completely cooled. Cut into bars. Store in refrigerator.