- In a bowl, combine all of the ingredients until smooth. Between two sheets of parchment paper, roll out the mixture until 1/8 inch (3 mm) thick. Freeze for 30 minutes.
- Remove the top piece of parchment paper. With a knife, cut out six 5 ½ x 1 ¼-inch (14 x 3.5 cm) rectangles. Freeze while you prepare the next steps.
Light Cream (Crème légère)
- In a small pot off the heat, whisk together the sugar, flour and cornstarch. Add the egg and egg yolk. Mix well. Add the milk and vanilla. Bring to a boil over medium heat, stirring constantly and scraping the bottom and sides of the pot, just until the mixture thickens. Remove from the heat. Pass through a sieve set over a bowl to remove any lumps.
- Cover with plastic wrap directly on the surface of the cream. Let cool, then refrigerate for 3 hours or until completely chilled. When ready to use the pastry cream, gently mix with a spatula until creamy and smooth.
- In another bowl, whisk the cream until firm peaks form. Using a whisk, fold the whipped cream into the pastry cream. Refrigerate the light cream until ready to assemble the éclairs.
- Meanwhile, in a pot, bring the water, milk, butter, sugar and salt to a boil. Remove the pot from the heat. Add the flour all at once and stir vigorously with a wooden spoon until the dough forms a ball and pulls away from the sides of the pot.
- Return the pot to medium heat and cook, stirring constantly, for 3 minutes or until the dough has dried out. This is a crucial step for perfect choux. The dough is sufficiently dried out when a thin film coats the bottom of the pot. Transfer to a mixing bowl or to the bowl of a stand mixer.
- Using a wooden spoon or the paddle attachment, add the eggs, one at a time, stirring between each addition, until the dough is smooth.
- With the rack in the middle position, preheat the oven to 375°F (190°C). Line a baking sheet with a silicone mat or parchment paper.
- Transfer the dough to a pastry bag fitted with a ¾-inch (2 cm) plain tip. On the baking sheet, pipe the dough into cylinders 5 ½ inches (14 cm) long and ¾ inches (2 cm) wide, evenly spacing them out.
- Place the rectangles of craquelins over the cylinders of dough, being careful not to crush them.
- Bake for 5 minutes. Reduce the oven temperature to 350°F (180°C). Bake for another 20 minutes or until nicely golden. Let cool completely on a wire rack. The pastries can be frozen at this step, if desired.
- Make a hole in each éclair by running the round handle of a wooden spoon from one end to the other (see note). Using a pastry bag fitted with a ½-inch (1 cm) plain tip, fill the hole of each éclair with the light cream.
- In a bowl large enough to dip the éclairs, melt the chocolate in the microwave oven for 1 to 2 minutes, stirring every 30 seconds. Whisk in the oil.
- Quickly dip the top of each éclair in the chocolate glaze, pivoting the pastry from side to side to get even coverage. Refrigerate for 30 minutes before serving. The éclairs will keep for 3 days in an airtight container in the refrigerator.
Instead of using the handle of a wooden spoon, you can pierce three holes in the bottom of each éclair using a 1/2-inch (1 cm) pastry tip.