Preheat oven to 350 degrees F. Grease and flour and 9x5 loaf pan.
Cream butter and granulated sugar in a large bowl until light and fluffy.
Add eggs one at a time, mixing well after each.
In a separate bowl, mix together flour, baking powder, and salt.
Add dry ingredients to creamed mixture alternately with 1/2 cup cider, mixing well after each addition.
Pour batter into pan and bake for 55-65 minutes, until a toothpick inserted into the center of the loaf comes out clean. In some ovens, it may even take a little longer because the center is so thick.
Mix together confectioners sugar and 4 T sparkling cider to form a smooth glaze.
Allow cake to cool, then pour glaze on top, allowing it to run down the sides.