Beat 1 cup butter at medium speed with an electric mixer until creamy; gradually add brown sugar, beating well. Stir in buttermilk mixture, eggs, and next 5 ingredients until blended. Spoon batter into greased muffin pans filling two-thirds full.
Bake at 350° for 20 to 23 minutes. Remove from pans immediately, and cool on wire racks.
Stir together powdered sugar, orange juice, and melted butter until smooth; drizzle glaze evenly over muffins.
Note: Batter may be covered tightly and stored in the refrigerator up to 24 hours.