Preheat oven to 375°. Line 2 rimmed baking sheets with parchment paper. Using a pencil, draw 10 (2 1⁄2-inch-long) evenly spaced lines onto each sheet of parchment paper; turn parchment paper over.
In a medium saucepan, bring to a boil together milk, butter, sugar, and salt over medium-high heat. Reduce to heat to low; add flour, stirring with a wooden spoon until a dough forms, approximately 2 minutes.
Transfer dough to the bowl of a stand mixer fitted with the paddle attachment. Beat on low for 1 minute to let cool. Increase mixer speed to medium, and beat in eggs and egg yolk, one at a time, until thoroughly incorporated. Beat for 2 minutes after adding egg yolk.
Transfer dough to a piping bag fitted with a large open-star tip (Ateco #826). Holding tip approximately 3⁄4-inch above parchment paper and working on one baking sheet at a time, apply even pressure to bag, and slowly pipe out dough in an oblong shape along each drawn line. Toward the end of each line, begin lessening pressure on piping bag. Stop applying pressure, and lift bag, leaving a small curl at end of piped dough. Using a wet finger, smooth curled tips, if necessary. Let stand at room temperature until ready to bake.
Bake one baking sheet at a time for 15 minutes. Rotate baking sheet, and bake until éclairs are fully puffed and golden brown, 10 to 15 minutes more. Remove from oven and let cool completely on baking sheets on wire racks.
Using a sharp knife, cut each éclair in half lengthwise. Place Whipped Ricotta Frosting in a piping bag fitted with a 1⁄4-inch French star tip (Ateco #864). Pipe desired amount of frosting into éclairs. Sprinkle frosting evenly with pistachios and chocolate chips. Serve immediately, or place in a covered container, refrigerate, and serve within 3 hours.
Notes
Make-Ahead Tip: Éclairs can be baked a week in advance, placed (unfilled) in a single layer in heavy-duty resealable bags, and frozen. Thaw completely before filling.
Recipe by TeaTime Magazine at https://teatimemagazine.com/whipped-ricotta-eclairs/