Combine rum and raisins in small measuring cup.
Cook on high (9) for 1 minute or until cup feels warm to the touch.
In glass baking dish, cook butter on high (9) for 1 minute or until butter is melted.
Sprinkle with graham cracker crumbs; lightly press into bottom of dish.
Layer chocolate pieces, raisins and rum, and walnuts.
Pour sweetened condensed milk evenly over the top.
Cook on medium (5) for 15 to 18 minutes or until lightly browned.
Cut into bars.