Pastry Cream (You can make this step the day before)

1. Cook the pastry cream: Add the the egg yolks and cornstarch to a 2-cup measuring cup or small bowl and whisk until smooth. Set aside.
2. Add the milk, half & half granulated sugar, and salt to a medium saucepan. Stirring frequently, bring to a simmer over medium heat (the mixture should have bubbles forming around the edges and be scalding hot).
3. Temper the eggs: Remove the pan from the heat and pour about 1/3 of the hot mixture into the egg yolks, and immediately whisk vigorously for about 30 seconds. This is called tempering the eggs. If you add the egg yolks directly to the hot mixture it will cook them and turn them into pieces of scrambled egg. 
4. Pour the egg mixture back into the saucepan and return the pan over medium heat. Whisk the mixture constantly until the mixture thickens, about 2 to 3 minutes. Remove the pan from the heat and whisk in the butter and vanilla.
5. Chill the pastry cream: Pour the pastry cream into a glass bowl. Place a piece of plastic wrap directly onto the top of the pastry cream. This keeps a skim from forming on top. Cool to room temperature and refrigerate the pastry cream at least 4 hours or overnight.

Pate a Choux (the dough)

1. Cook the Pate a Choux (dough): Add the butter, water, sugar, and salt to a medium saucepan over medium heat. Cook until the butter melts and comes to a simmer around the edges. Using a wooden spoon, add the flour all at one time and quickly stir it in. Continue stirring constantly, until the mixture pulls away from the sides of the pan, and there is a film on the bottom of the pan, about 1  minute. The dough should come together and form a loose ball.
2. Mix the Pate a Choux (dough): Stand Mixer – Transfer the dough to the bowl of a stand mixer. Mix on low speed until the dough has slightly cooled, about 1 minute. It should be no more than slightly warm. If the dough is too hot it will cook the eggs. Increase speed to medium. Add the eggs one at a time, mixing thoroughly after each addition. Make sure to only add one egg at a time and thoroughly mix before adding the next egg. The dough cannot absorb all of the eggs at one time. The egg and dough will separate at first but don’t worry, they will come back together.  Once it’s mixed, mix for about 1 additional minute.  The finished dough should be smooth and silky.                                                          
3. Cream Puff Templates: Cut two pieces of parchment paper big enough to fit two large cookie sheets. Using a 2-inch round cookie or biscuit cutter and a pencil, trace circles onto the parchment paper, leaving plenty of room between them. Try to draw about 9 circles on the parchment paper, making sure they are plenty dark enough. This will be your piping template. This recipe will make between 18 to 20 cream puffs. Turn the templates upside down, (pencil face down) in each pan. 
4. Preheat oven to 425 degrees.
5. Piping: Using a large round piping tip, (I used Wilton 2A, but you can also use a 1A), pipe 2-inch rounds of the dough, about 1-inch high onto the circle templates. Here’s how: Place the piping bag perpendicular (straight up and down) to the parchment paper, holding the tip over the center of the circle. Apply even pressure, allowing the cream puffs to expand in both width and height. When you’re finished piping one, do not pull the tip straight up. Instead, swirl the tip when you are done and quickly pull away. After you’ve piped all of them, dip your finger tip in water and gently tap on the point of the swirl to smooth it. 
6. Egg wash: Whisk together the egg and water. Gently brush the egg wash over the top of each cream puff.
7. Baking: Bake the cream puffs for approximately 30 to 35 minutes, until they are golden brown on top. DO NOT OPEN THE OVEN DOOR WHILE THEY ARE BAKING! Cool air will cause them to collapse. Once they are baked, allow them to cool completely on the baking sheets.  
8. Finishing the pastry cream: Remove the pastry cream from the refrigerator. Use a whisk to break up the cold pastry cream and make it smooth. Whip the 1 cup of heavy whipping cream in a stand mixer until it’s very thick. Fold the pastry cream into the whipped cream.
9. Assembling the pastry shells:  Attach a star tip to a piping bag and fill the bag with the pastry cream. Using a serrated knife, cut the tops off of the cooled pastry shell. If you prefer, you can remove some of the soft strands inside. Pipe the pastry cream into each pastry shell and place the top. Dust the tops with powdered sugar. 
10. Cream Puffs are best the day they’re made. However, they are still pretty yummy the next day, just not quite as crispy.