Preheat oven to 450 degrees F (230 degrees C). Grease a cookie sheet.
In a medium saucepan, combine 1/2 cup butter and 1 cup water. Bring to a boil, stirring until butter melts completely. Reduce heat to low, and add flour and salt. Stir vigorously until mixture leaves the sides of the pan and begins to form a stiff ball. Remove from heat. Add eggs, one at a time, beating well to incorporate completely after each addition. With a spoon or a pastry bag fitted with a No. 10, or larger, tip, spoon or pipe dough onto cookie sheet in 1 1/2 x 4 inch strips.
Bake 15 minutes in the preheated oven, then reduce heat to 325 degrees F (165 degrees C) and bake 20 minutes more, until hollow sounding when lightly tapped on the bottom. Cool completely on a wire rack.
For the filling, combine pudding mix and milk in medium bowl according to package directions. In a separate bowl, beat the cream with an electric mixer until soft peaks form. Beat in 1/4 cup confectioners' sugar and 1 teaspoon vanilla. Fold whipped cream into pudding. Cut tops off of cooled pastry shells with a sharp knife. Fill shells with pudding mixture and replace tops.
For the icing, melt the chocolate and 2 tablespoons butter in a medium saucepan over low heat. Stir in 1 cup confectioners' sugar and 1 teaspoon vanilla. Stir in hot water, one tablespoon at a time, until icing is smooth and has reached desired consistency. Remove from heat, cool slightly, and drizzle over filled eclairs. Refrigerate until serving.