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.