In bowl sift together flour, sugar, baking powder and salt. Cut in shortening until mixture resembles coarse meal; stir in chocolate chips and 1/2 cup of macadamia nuts. In a small bowl combine egg, milk and rum; add this mixture to the flour mixture. Stir batter until it is just combined. Divide the batter among 12 buttered or paper lined muffin tins. Sprinkle tops with the remaining 1/4 cup macadamia nuts and bake for 25 minutes in preheated 400ºF. oven. Let muffins cool in the tins for 5 minutes then turn them out onto a rack. Yield 12 muffins.