Combine cream, milk, ⅓ cup granulated sugar, vanilla bean, and salt in a medium saucepan. Place on stovetop over medium heat. Stir frequently until sugar is dissolved and mixture comes to a simmer. Remove from heat and allow to cool for 10 minutes.

In a separate large bowl, whisk together egg yolks and 3 Tablespoons of sugar for about 15 seconds until sugar begins to dissolve.

Sprinkle cornstarch over the egg/sugar mixture and whisk until combined and slightly thickened.

Slowly drizzle about ⅓ cup of the cream mixture into the egg mixture while whisking constantly. Then gradually whisk in the remaining cream mixture until fully combined.

Pour the mixture back into the saucepan and return to stovetop over medium heat. Whisk frequently until thickened.

Remove from heat and pour mixture through a fine mesh strainer into a heatproof bowl. Discard the vanilla bean.

Whisk in butter, one piece at a time until completely combined.

Place plastic wrap directly on the surface of the pastry cream to avoid skin formation. Cool at room temperature for 30 minutes, then refrigerate for at least 2-4 hours.

Preheat oven to 400°F (200°C) and line a large baking sheet with parchment paper.

Combine water, butter, and salt in a saucepan over medium heat and bring to a rolling boil.

Add flour to the boiling mixture and stir continuously until it forms a ball and pulls away from the pot sides.

Remove from heat and let cool for several minutes. Add eggs one at a time, stirring well after each addition until smooth.

Transfer choux pastry to a piping bag and pipe mounds about 2 inches wide by 1 inch tall onto the prepared baking sheet.

Bake in the oven for 30 minutes or until golden brown. Pierce the lower center of each cream puff with a knife and return to the oven for an additional 10 minutes with the oven door cracked.

Remove from oven and cool completely on the baking sheet.

Fill each cream puff with pastry cream using a piping bag.

Dust the tops with powdered sugar just before serving.