Preheat oven to 350 degrees F (175 degrees C). Grease and flour 12 muffin cups.
In a large bowl, cream together the melted butter and sugar until smooth. Beat in the eggs one at a time, then stir in the vanilla. Combine the flour, baking soda and salt; stir into the creamed mixture alternately with the buttermilk.
Fold in 1 cup of pistachios. Fill muffin cups about 2/3 full.
Bake for 20 to 25 minutes in preheated oven. Sprinkle remaining pistachios on top of muffins before baking. Bake for an additional 5 minutes.
Cool in pans for 10 minutes before removing to cool completely on wire racks.