Heat oven to 350°F. Generously grease and flour two 9-inch round cake pans.** In small saucepan over low heat, melt 2/3 cup butterscotch chips in 1/4 cup water, stirring until smooth. Cool slightly.
Lightly spoon flour into measuring cup; level off. In large bowl, combine flour, all remaining cake ingredients and cooled butterscotch mixture; beat at low speed until moistened. Beat 3 minutes at medium speed. Pour batter into greased and floured pans.
Bake at 350°F. for 20 to 30 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pans. Cool 30 minutes or until completely cooled.
In medium saucepan, combine 1/2 cup sugar and cornstarch; stir in half-and-half, 1/3 cup water, 1/3 cup butterscotch chips and 1 egg. Cook over medium heat until mixture thickens, stirring constantly. Remove from heat. Stir in margarine, coconut and nuts; cool slightly.
In small bowl, beat whipping cream until soft peaks form. Gradually add brown sugar and vanilla, beating until stiff peaks form.
To assemble cake, place 1 cake layer, top side down, on serving plate. Spread with half of filling mixture. Top with second layer, top side up; spread remaining filling on top to within 1/2 inch of edge. Frost sides and top edge of cake with seafoam cream. Refrigerate at least 1 hour before serving. Store in refrigerator.