Making the Pastry:

1. Preheat the oven: Begin by preheating your oven to 425°F (220°C). Line a baking sheet with parchment paper to prevent the cream puffs from sticking.
2. Sift dry ingredients: Sift the flour, salt, and baking soda into a bowl and set it aside. Sifting the dry ingredients ensures there are no lumps and that everything is evenly distributed.
3. Cook the dough: In a medium saucepan, combine the water and butter over medium heat. Stir the mixture occasionally until the butter is melted, and the water starts to simmer. Once the butter is fully melted, remove the saucepan from the heat and add the sifted flour mixture all at once. Stir vigorously with a wooden spoon until the mixture becomes smooth and begins to pull away from the sides of the pan. This is a critical step to creating the structure of the dough.
4. Incorporate the eggs: After the flour mixture is fully incorporated and the dough has thickened, return the saucepan to low heat. Add the eggs one at a time, beating with a wooden spoon or hand mixer after each addition. It’s important to fully incorporate each egg before adding the next one. This will ensure that the dough becomes smooth and shiny.
5. Shape the puffs: Once the dough is fully mixed, transfer it to a pastry bag fitted with a ½-inch round tip. On the prepared baking sheet, pipe out 3-inch puffs, spacing them about ½ inch apart. These will expand in the oven, so be sure to leave enough room for them to rise.
6. Bake the pastry: Place the baking sheet in the preheated oven and bake for 20 minutes or until the cream puffs are golden brown. Resist the temptation to open the oven during the first 10 minutes of baking to allow the puffs to rise properly. Once baked, carefully slit the side of each cream puff with a knife to let out the steam. This step prevents the puffs from becoming soggy inside.
7. Cool the pastry: Transfer the baked cream puffs to a wire rack and let them cool completely before filling them with custard.

Making the Custard Filling:

1. Prepare the custard base: In a medium saucepan over moderate heat, combine the sugar, flour, and salt. Gradually add the milk, stirring constantly. Bring the mixture to a boil, and continue cooking and stirring until the custard thickens and begins to bubble. This should take about 5 minutes.
2. Temper the eggs: In a separate bowl, beat the egg yolks. Slowly add a little of the hot milk mixture to the egg yolks, whisking constantly to temper the eggs. Once the egg yolks are warmed up, pour the mixture back into the saucepan with the remaining milk mixture.
3. Cook the custard: Return the saucepan to the heat and cook the custard over low heat, stirring continuously, for another 2 minutes until it thickens further. The custard should coat the back of a spoon and have a silky consistency.
4. Finish the custard: Remove the saucepan from the heat and stir in the butter, vanilla extract, and rum. The butter adds a smooth richness to the custard, while the vanilla and rum provide aromatic depth.
5. Cool the custard: Transfer the custard to a shallow bowl, covering the surface with plastic wrap to prevent a skin from forming. Refrigerate the custard until it’s completely cooled, about 1–2 hours.

Assembling the Cream Puffs:

1. Fill the puffs: Once the pastry shells and custard are completely cooled, cut a small slit into the side of each cream puff. Fill a pastry bag fitted with a large round tip with the cooled custard. Pipe the custard generously into each puff until they are filled to the brim.
2. Garnish: For a traditional touch, top each cream puff with a maraschino cherry and a dusting of powdered sugar.
3. Serve and enjoy: These Italian cream puffs are best served chilled, allowing the custard to stay firm and the pastry to remain crisp. They make for an impressive dessert at any gathering, especially during festive occasions like St. Joseph’s Day.