In a small bowl, dissolve yeast in warm water. Let stand until creamy, about 10 minutes. Warm the milk in a small saucepan until it bubbles, then remove from heat. Mix in 1 cup butter until melted. Let cool until lukewarm.
In a large bowl, beat together the eggs and 1 1/2 cups sugar. Mix in the nutmeg, orange extract, vanilla extract, and the yeast mixture. Stir in 3 cups flour and the salt. Stir in 1/3 of the milk mixture. Mix in the remaining flour and milk mixture in two alternating additions. Cover bowl, and let rise until doubled, about 45 minutes.
In a small bowl, prepare the topping by cutting together 1/2 cup butter and 2/3 cups sugar until mixture resembles coarse crumbs.
Preheat oven to 350 degrees F (175 degrees C). Lightly grease 3 10-inch Bundt pans.
Divide dough into the prepared pans, and sprinkle with the topping mixture.
Bake in preheated oven for 30 to 40 minutes, until a toothpick inserted into center comes out clean.