1. Prepare the Choux Pastry: Combine milk, water, butter, and salt in a pot and bring to a boil. Add flour and stir until the dough forms a ball. Cool the dough, then mix in eggs one at a time until smooth and glossy.
2. Preheat the Oven: Set your oven to 200°C (400°F) to prepare for baking.
3. Pipe the Batter: Use a piping bag to form 2-inch rounds of choux batter on a baking sheet lined with parchment paper.
4. Add Craquelin: Place a disc of craquelin dough on top of each choux puff and gently press it down.
5. Bake the Puffs: Bake at 200°C (400°F) for 15 minutes, then reduce to 180°C (350°F) and bake for an additional 30-35 minutes until golden.
6. Prepare the Pastry Cream: Heat milk in a saucepan. Separately, whisk egg yolks, sugar, and cornstarch. Gradually combine the mixtures. Cook until thickened, remove from heat, and add butter and vanilla. Cool completely.
7. Whip the Cream: Whip heavy cream until soft peaks form, then fold it into the cooled pastry cream for a lighter filling.
8. Fill the Puffs: Make a small cut in each puff or remove the top. Use a piping bag to fill them with cream.
9. Serve Fresh: Serve the cream puffs immediately for the best texture and taste.
10. Store if Necessary: Store unfilled puffs in an airtight container or freeze for later use. Refrigerate filled puffs and consume them within a day.