Preheat oven to 425 degrees F. Line two baking sheets with parchment paper, set aside.

To make the choux pastry, combine the water, butter and salt in a large saucepan over medium-high heat, and bring to a boil. Remove the pan from the heat, and add the flour all at once while constantly stirring vigorously with a wooden spoon. Return the pot to the stove and cook over medium heat, stirring constantly until the mixture is smooth, glossy and pulls away from the sides, about 3 minutes.

Remove the pan from the heat, and transfer the dough into the bowl of your stand mixer and let it cool down for about 10 minutes. Using the paddle attachment, beat the mixture on low for about a minute. Add in the eggs, one at a time, beating for about a minute after each addition. The batter will be smooth and glossy. Make sure to beat the mixture for 2 minutes after adding the last egg. Stop the mixer and let cool down to room temperature. You want to make sure the choux pastry isn't warm at all before adding in the chocolate chips. Fold them in at the very last minute, so that they don't melt and leave streaks throughout the pastry.Transfer to a large disposable piping bag, fitted with a medium plain circle tip.

Pipe out small rounds, evenly spaced out, onto the prepared baking sheets, making sure to leave space because they do grow. Bake for 15 minutes, then reduce temperature to 350 degrees F and continue baking for another 20 minutes. They should be a medium golden brown and sound hollow. It's important to not open the oven door while the puffs are baking because if you do, you run the risk of them deflating from the change in temperature. Once done, remove the baking sheets from the oven and transfer to a wire rack to cool.

To make the custard cream filling, combine 1 cup half and half, 3 tablespoons sugar and a pinch of salt in a medium saucepan; bring to a simmer. Combine 2 1/2 tablespoons sugar, cornstarch, egg and egg yolks in a medium bowl, stirring with a whisk until completely smooth. Gradually drizzle warm milk mixture into the egg mixture, whisking nonstop. Pour the mixture back into the saucepan and cook over medium heat until mixture thickens, about 4 minutes, whisking constantly. Remove from heat, and whisk in the butter and vanilla extract. Pour the mixture into a bowl through a fine mesh strainer to remove any lumps. Cover the top directly with plastic wrap and then let chill in the fridge or freezer until completely cooled down. Once cool, fold the whipped cream into the custard in batches until smooth. Transfer this mixture into a piping bag.

Cut each cream puff in half using a serrated knife. Then pipe out the cream filling onto each bottom, sandwiching together with the top half of the pastry. You could also just spoon the mixture into the puffs if you don't have a piping bag.

To make the topping, combine corn syrup, 1 tablespoon half and half and 1 teaspoon vanilla extract in a heat proof bowl. Heat in the microwave on high for 15 seconds. Add in the powdered sugar and cocoa powder and whisk until smooth. The glaze will be thick and sticky. Pour over each pastry and allow to set before serving. Cream puffs are best when eaten the day of but leftovers can be kept in the fridge for the next day. Enjoy!