Combine the milk, ? cup cream, and scraped vanilla seeds in a medium pot and heat over medium-high heat while whisking occasionally. Bring to a boil and turn off the heat.

In a large bowl, whisk together sugar, cornstarch, and salt, then add egg yolks and whisk until pale yellow and smooth. Slowly pour in ? cup of the hot milk mixture while whisking, then whisk in the remaining hot milk mixture and strain back into the saucepan.

Cook the egg yolk mixture over medium-high heat, whisking constantly, until thickened and bubbling. Remove from heat and whisk in butter until melted. Transfer to a bowl, cover with plastic wrap, and chill for at least 2 hours.

Preheat the oven to 425?F and line a baking sheet with parchment paper.

In a large saucepan, bring water, butter, sugar, and salt to a boil over medium-high heat. Remove from heat and stir in flour until incorporated. Return to medium heat and cook, stirring for about 60 seconds.

Transfer the mixture to a stand mixer and beat on medium speed for about 2 minutes to cool. Add eggs one at a time, mixing until smooth and glossy. If dough is still clinging to the beater, add the last egg and mix.

Transfer dough to a pastry bag fitted with a large round tip. Pipe dollops of dough approximately 2 inches in diameter onto the baking sheet. Tap down any spikes.

Bake for about 20 minutes until golden brown and dry. Do not open the oven during baking. After 20 minutes, poke holes in the side of each puff and return to the oven for another 3 minutes. Let them cool completely on the baking sheet.

In a bowl, beat the remaining 1 cup cold cream until stiff peaks form. Whisk the chilled custard to smooth the texture and fold in the whipped cream. Transfer the filling to a pastry bag fitted with a star tip.

Cut the tops off the cooled puffs and pipe the cream filling inside. Replace the tops and dust with confectioners? sugar. For best results, serve within a few hours.

Store leftovers in an airtight container in the fridge for up to 2 days.