Source: "So This Is Kosher" by Ann Kaye and Hetty Rance, 1986
Pipe pastry through a 3/4" plain tip, 3" long onto a greased baking pan; use a knife to smoothly cut each eclair free from the bag. Bake in 425F oven for 10 minutes, then reduce heat to 375F and bake 15- 20 minutes until well-risen and brown. Make a slit in one long side of each eclair to allow steam to escape, then cool on rack.
Melt the chocolate with the oil in the top of a double boiler. Mix the sugar with the hot water, and stir into melted chocolate. Beat well until smooth and thick enough to coat the back of a spoon. Keep warm.
Pipe or spoon the whipped cream into the slits in the sides of the eclairs, then spread the icing on top. Leave until set.