Combine 3-1/2 cups flour, remaining sugar, nutmeg and salt, and sift into a large mixing bowl. Stir in lemon zest. Separate center of mixture to form a hole and pour in yeast mixture and milk. Add egg yolks and using a wooden spoon, combine dry ingredients into the yeast/milk mixture. When mixture is smooth, beat in 8 tablespoons butter (1 tablespoon at a time) and continue to beat 2 minutes, or until dough can be formed into a medium-soft ball.