Combine first 3 ingredients in saucepan and cook until butter melts.
Beat buttermilk, eggs, vanilla until smooth . Mix buttermilk mixture with butter mixture. Add sugar and flour. Beat till blended. Mixture will be thin.
Coat 3 8" pans with non-stick spray. Line with wax paper. Pour batter evenly in 3 pans. Bake at 350 degrees for 22-25 minutes. Cool in pans for a few minutes then remove from pan and let cool completely.
Spread chocolate filling between layers and on sides chill cake 30 minutes. Pour frosting over top of cake. Let it run down sides.
CHOCOLATE FILLING: melt 1package semi sweet chocolate chips, 1/3 cup whipping cream 1/4 stick of butter in microwave. Add about 1/2-3/4 cup powdered sugar. Whisk till smooth. Cool and whisk ever so often till is thickens. Spread between cake layers but not on top of cake.
FROSTING : In a saucepan combine 1/4 cup butter or margarine, 1cup brown sugar, and 1/3 cup whipping cream. Cook over medium heat, stirring often. Let it come to a boil and then time boiling for 1 minute. Remove from heat . Add 1cup powdered sugar and vanilla. Whisk till smooth. Add 1 cup pecans. Stir until thickened...about 2-4 minutes. Pour over top of cake and let it run down sides.