Melt the white chocolate in water over low heat until smooth. Whip the cream until frothy, then gradually add the sugar mixture while beating.
Cream the butter in a large bowl and blend in the melted white chocolate.
In another bowl, sift together flour, salt, and baking soda.
To the chocolate and butter mixture, add the flour mixture, sugar, and buttermilk; beat for 2 minutes.
Add eggs one at a time, beating well after each addition.
Stir in vanilla, then gently fold in chocolate chips, chopped pecans, and shredded coconut.
Divide the batter between two well-greased and floured 9-inch cake pans and bake at 350°F for 30 minutes.
Cool the cakes in pans for 10 minutes before removing and allow them to cool completely.
While the cakes bake, prepare the chocolate custard by combining sugar and flour, then beating into eggs.
Stir in the melted chocolate.
Pour the egg mixture into scalded milk in a double boiler, cooking and stirring frequently until thick.
Add vanilla and caramels and continue stirring until caramels are melted.
Let the custard cool fully.
For the frosting, sift sugar and cocoa together and blend in vanilla.
To assemble the cake, place one cake layer on a serving plate and drizzle with crème de cacao.
Spread the cooled custard evenly over this layer, stopping about 1/4 inch from the edge.
Place the second cake layer on top and frost the entire cake.
Finish with chocolate sprinkles.
Use strips of wax paper around the edges of the plate while frosting to keep the presentation clean, then gently remove them after decorating.