Preheat oven to 375°. Line 2 greased 9-in. round baking pans with waxed paper; set aside. In a microwave, melt butterscotch chips with 1/4 cup water at 70% power for 1 minute; stir. Microwave at additional 10- to 20-second intervals, stirring until smooth. Cool to room temperature., In a large bowl, cream shortening and sugars until light and fluffy, 5-7 minutes. Add eggs, 1 at a time, beating well after each addition. Beat in butterscotch mixture. Combine the flour, baking soda, baking powder and salt; add to creamed mixture alternately with buttermilk just until combined., Pour into prepared pans. Bake until a toothpick inserted in the center comes out clean, 25-30 minutes. Cool for 10 minutes before removing from pans to wire racks to cool completely., In a large saucepan, combine sugar and cornstarch. Stir in evaporated milk and water until smooth. Cook and stir over medium heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer. Remove from the heat. Stir a small amount of hot filling into egg yolk; return all to the pan, stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer. , Remove from the heat. Gently stir in chips and butter. Stir in pecans and coconut. Cool to room temperature without stirring., Place 1 cake layer on a serving plate; spread with half of the filling. Top with second layer and remaining filling. Frost sides with buttercream frosting. Store in the refrigerator.