Preheat oven to 350 degrees. Grease and flour 2 9-inch cake pans. Line bottom of the pan with parchment paper.
In a large bowl or standing mixer, cream butter until light and fluffy. Add sugar and beat until creamy. Add eggs, one at a time, beating well after each addition. Stir in melted chocolate.
In a separate bowl, combine four and salt. Add buttermilk and chocolate mixture, alternating. Stir in vanilla.
In a small bowl, dissolve baking soda in vinegar. Slowly add this to the chocolate mixture. Mix just until blended. Do not over-mix.
Pour batter into prepared pans and bake for 30-35 minutes or until a toothpick inserted in center comes out clean. Cool in pans for 10 minutes then remove from pans. Transfer to wire racks and cool completely before frosting.
Chocolate Frosting
In a large mixing bowl, cream butter until light and fluffy. Slowly add sugar, 1/2 cup at a time, beating well between additions. Stir in chocolate and vanilla. If necessary, thin frosting with 1-2 tsps. half-and-half.
ENJOY!!!