In the bowl of an electric mixer cream the butter and brown sugar.
Add the egg and beat well.
In a glass measuring cup combine the buttermilk and baking soda. Set aside.
In a separate bowl, mix together the flour, cinnamon, nutmeg, and allspice.
Add the flour mixture to the creamed mixture alternately with the buttermilk mixture, beginning and ending with the flour.
Stir in the apple butter and chopped pecans.
Pour into a greased 9-in x 5-in x 3-in loaf pan.
Bake at 350 F for 1 hour and 5 minutes, or until a toothpick inserted in the center comes out clean.
Cool in the pan for 5 minutes, then remove to a wire rack to cool completely.
For the Glaze: Mix together the powdered sugar, butter, cinnamon, vanilla, and enough milk to reach your desired consistency.
Drizzle over the bread and allow to cool completely.