Preheat oven to 325 degrees. Grease and flour three 8-inch pans. In a large bowl, cream 1-cup butter with sugar. Add eggs one at a time, beating well after each addition and add and mix cocoa. Add flour alternately with buttermilk. Add vanilla and salt. Mix baking soda with vinegar, and gently stir into mixture. Be careful not to over mix. Divide batter into three prepared 8 inch round pans. Bake at 325 degrees for 25 minutes. Allow cooling. To make the White Chocolate Cream Cheese Icing: Melt the white chocolate and allow cooling to lukewarm. In a large bowl, beat the cream cheese until light and fluffy. Gradually beat in melted white chocolate and softened butter. Beat until it is the consistency of whipped cream, and then use to fill and frost the cake.