Break off and discard stems of collards. Wash leaves thoroughly. Slice leaves into bite-size pieces by rolling several leaves together and cutting into 1/4 inch strips. Blanch greens in boiling water for 30 minutes; drain well. Melt drippings in large skillet, or heat oil; add onion and cook until tender. Stir in tomato and cook until just tender. Add greens to onion mixture and stir until well coated. Cook until tender. Stir in a pinch of nutmeg.