In medium saucepan heat milk slowly just until bubbles form around the edge. In a small bowl, combine sugar and cornstarch, mixing well. Stir into hot milk all at once. Cook, stirring, over medium heat until mixture boils. Reduce heat and simmer 1 minute. Beat a small amount of mixture into egg yolks. Pour back into saucepan and cook, stirring, over medium heat until mixture boils and thickens. Stir in vanilla. Place waxed paper on the surface to prevent skin from forming. Refrigerate until ready to use. Makes 3 cups.
Will fill 12 Eclairs. Bring water, butter, and salt to boil. Remove from heat and stir in flour. Beat over low heat until mixture leaves sides of the pan. Remove from heat. Beat in eggs, one at a time. Beat until shiny and satiny and broken in strands. Drop three inches apart on ungreased sheet. Form 12 strips 4 x 1 inches. Bake at 400F for 35 to 40 minutes. (Will sound hollow when tapped, you should keep it from drafts).
In a small saucepan heat the chocolate chips and shortening. Heat until all is melted. Add corn syrup and milk to the sauce. Stir until the mixture is uniform.
Cut the eclair shells in half, fill the shell with cream, and drizzle chocolate glaze on top. Store in an airtight container in the refrigerator.