Follow these detailed steps carefully to achieve perfectly puffed, golden-brown shells and a luscious, stable filling. The process is divided into four main stages: making the dough, baking the shells, preparing the filling, and assembly.

Part 1: Making the Pâte à Choux Dough

1. Prepare Your Workstation: Preheat your oven to 400°F (200°C). Line two large baking sheets with parchment paper. This prevents the puffs from sticking and ensures even baking. Set them aside.
2. Melt the Base: In a medium-sized, heavy-bottomed saucepan, combine the water, cubed unsalted butter, granulated sugar, and salt. Place the pan over medium heat.
3. Bring to a Boil: Stir occasionally until the butter is completely melted. Bring the mixture to a rolling boil. You want to see vigorous bubbles across the entire surface.
4. Add the Flour: As soon as the mixture is boiling, remove the pan from the heat immediately. Add the entire cup of sifted all-purpose flour all at once.
5. Stir Vigorously: Using a sturdy wooden spoon or a heat-resistant spatula, stir the mixture vigorously. The dough will be very thick at first. Keep stirring until the flour is fully incorporated and the mixture forms a thick, cohesive ball of dough that pulls away cleanly from the sides and bottom of the saucepan. This process should take about 1-2 minutes. A thin film may form on the bottom of the pan; this is normal.
6. Cook the Dough: Return the saucepan to the stove over low heat. Continue to stir and cook the dough ball for an additional 2 minutes. This step is crucial as it cooks off excess moisture from the flour, which helps the puffs to rise better and develop a sturdier structure.
7. Cool the Dough: Transfer the hot dough to the bowl of a stand mixer fitted with the paddle attachment (or a large mixing bowl if using a hand mixer). Beat the dough on low speed for 3-5 minutes. The goal is to release steam and cool the dough down to just warm to the touch. It should not be hot enough to scramble the eggs you are about to add.

Part 2: Incorporating the Eggs and Piping the Puffs

1. Add Eggs One at a Time: With the mixer still on low speed, add the room temperature eggs one at a time. It is critical that you wait for each egg to be fully and completely incorporated into the dough before adding the next one. The dough may look separated or curdled after each addition, but keep mixing, and it will come back together into a smooth, glossy paste.
2. Check for Consistency: After adding the fourth egg, stop the mixer and check the dough’s consistency. It should be thick, smooth, and glossy. When you lift the beater, the dough should fall off in a slow, thick ribbon, forming a “V” shape that holds for a few seconds. If the dough is too stiff, you can whisk a fifth egg in a separate bowl and add a small amount of it at a time until the desired consistency is reached.
3. Prepare for Piping: Transfer the finished pâte à choux dough to a large piping bag fitted with a large round tip (about ½-inch or 1.5 cm in diameter). You can also use a star tip for a more decorative look.
4. Pipe the Puffs: Pipe the dough onto the prepared baking sheets. For medium-sized cream puffs, pipe mounds that are about 1.5 inches in diameter and 1 inch high. Be sure to space them about 2-3 inches apart, as they will expand significantly during baking.
5. Smooth the Tops: The piped mounds may have a small peak on top. To prevent this from burning, dip your finger in a little water and gently press down the tip of each mound to smooth it out.

Part 3: Baking the Puffs to Perfection

1. Initial High-Heat Bake: Place the baking sheets in the preheated 400°F (200°C) oven. Bake for 20 minutes. This initial burst of high heat causes the water in the dough to turn into steam rapidly, forcing the puffs to rise. Do not open the oven door during this time, as the sudden drop in temperature can cause them to collapse.
2. Reduce Heat and Continue Baking: After 20 minutes, without opening the oven door, reduce the oven temperature to 350°F (175°C). Continue to bake for another 10-15 minutes. This second, lower-temperature phase is for drying out the interior of the shells and setting their structure. The puffs should be a deep, golden brown color and feel very light and hollow. Under-baked puffs will be soft and will collapse as they cool.
3. Vent the Puffs: Once the puffs are a deep golden brown, remove them from the oven. Working quickly, use a small sharp knife or a skewer to pierce the side or bottom of each puff. This allows any remaining steam trapped inside to escape, ensuring the interior stays dry and crisp rather than becoming soggy.
4. Final Drying (Optional but Recommended): For extra-crisp shells, turn the oven off completely. Return the pierced puffs to the warm oven, prop the oven door open slightly with a wooden spoon, and let them sit for another 10-15 minutes to dry out completely.
5. Cool Completely: Transfer the baked and vented choux shells to a wire rack to cool completely before filling. They must be at room temperature before you add the cream.

Part 4: Preparing the Strawberry Cream and Assembly

1. Prepare the Cream Base: In a large, chilled mixing bowl, combine the very cold heavy whipping cream, sifted powdered sugar, and vanilla extract. Using a stand mixer with a whisk attachment or a hand mixer, beat the mixture on medium-low speed until it starts to thicken.
2. Whip to Stiff Peaks: Increase the speed to medium-high and continue to beat until stiff peaks form. A stiff peak will hold its shape completely and will not droop when the beaters are lifted. Be careful not to over-beat, or the cream will turn into butter.
3. Fold in the Strawberries: Gently fold the finely diced fresh strawberries into the whipped cream using a spatula. Mix until they are just evenly distributed. Do not overmix, as this can deflate the cream.
4. Fill the Puffs: There are two common methods for filling the cream puffs.
   • Method 1 (Slicing): Using a serrated knife, carefully slice each cooled puff in half horizontally, like a hamburger bun. Spoon or pipe a generous amount of the strawberry whipped cream onto the bottom half, then place the top half back on.
   • Method 2 (Piping): Transfer the strawberry cream to a piping bag fitted with a smaller round tip. Pierce a hole in the bottom of each cooled puff with the tip of the piping bag or a small knife. Pipe the filling directly into the center of the puff until it feels full and heavy.
5. Garnish and Serve: Arrange the filled cream puffs on a serving platter. Just before serving, dust them generously with powdered sugar. For an extra touch, top each puff with a fresh strawberry slice. Serve immediately for the best texture.