Combine the first 6 ingredients in a large bowl, and make a well in center of mixture. Combine buttermilk and molasses; stir well. Add to flour mixture, stirring just until moistened. Fold in currants and walnuts.
Spoon the mixture into a 13-ounce coffee can coated with cooking spray. Cover with aluminum foil coated with cooking spray; secure foil with a rubber band. Place the can in an electric slow cooker; add enough hot water to cooker to come halfway up sides of can. Cover with lid, and cook on high-heat setting for 2 hours and 50 minutes or until a wooden pick inserted in center comes out clean. Remove can from water. Let bread cool, covered, in can on a wire rack for 5 minutes. Remove bread from can, and let cool completely on wire rack.