Preheat your oven to 375°F (190°C). In a medium saucepan, combine 1 cup of water and ½ cup of butter over medium heat until the butter melts. Add 1 cup of all-purpose flour and a pinch of salt, stirring until the mixture forms a ball and pulls away from the sides, about 2-3 minutes.

Remove from heat and let the dough cool slightly for about 5 minutes. Beat in 4 eggs one at a time until the dough is smooth and glossy.

Line a baking sheet with parchment paper. Transfer the dough to a piping bag and pipe 1.5-inch rounds, spaced about 2 inches apart. Bake for 25-30 minutes until golden and puffed.

Once baked, let the cream puffs cool on a wire rack.

In a medium saucepan, combine 2 cups of milk, ½ cup of sugar, and ⅓ cup of cornstarch over medium heat. Stir until thickened, about 5-7 minutes. Remove from heat and stir in 4 egg yolks and 1 tsp of vanilla extract.

Once cooled, gently cut a small slit in each puff and fill with custard.

Dust filled cream puffs with powdered sugar or drizzle chocolate ganache if desired.

Arrange cream puffs on a platter and refrigerate for at least 30 minutes before serving.