Wash yams and cut in half lengthwise. Place in a in a plastic bag without drying.
Microwave on high for 10 minutes. If your microwave doesn't rotate while cooking, turn the bag once or twice during cooking. Cool slightly.
Peel yams and cut in flat, lengthwise slices. About 1/2 inch thick.
Butter a 9 of 10 inch round baking dish. Arrange a layer of yam slices in dish.
Arrange a layer of apple slice on top of yams. Sprinkle with 1/2 Tbsp. lemon juice.
Mix together brown sugar, salt, mace, cinnamon and pecans. Cover apples with half of this mixture and drizzle with half the butter.
Repeat all the layers. Cover with plastic wrap and microwave on high for 15 minutes. If your microwave doesn't rotate, turn the dish 2 to 3 times during cooking.
NOTE: To microwave whole yams or sweet potatoes: 1 yam-5-6 minutes, 2 yams- 8-11 minutes, 3 yams- 12-15 minutes, 4 yams-19 minutes ** Just be sure to pierce the yams or sweet potatoes several times with a fork before microwaving so they don't explode.
***You can substitue sweet potatoes for the yams. It doesn't change the directions.