01 -  Preheat oven to 390°F. Line two baking sheets with parchment paper. 
 02 -  In a saucepan over medium heat, combine water, whole milk, butter, sea salt, and sugar. Bring to a boil. 
 03 -  Add flour all at once and stir vigorously until dough pulls away from the sides and forms a ball, about 1–2 minutes. 
 04 -  Transfer dough to a mixing bowl and allow to cool for 5 minutes. Beat in eggs one at a time until the mixture is smooth and glossy. 
 05 -  Transfer dough to a piping bag fitted with a large star tip. Pipe 8 rings about 3 inches in diameter onto prepared sheets, spacing apart. Bake for 25–30 minutes until golden and puffed. Cool completely on a wire rack. 
 06 -  Heat whole milk with split vanilla bean (seeds scraped in) or vanilla extract in a saucepan until just boiling. Remove from heat. 
 07 -  In a bowl, whisk together egg yolks and granulated sugar until pale. Add cornstarch and whisk until smooth. 
 08 -  Gradually whisk hot milk into egg yolk mixture. Return to saucepan and cook over medium heat, whisking constantly, until thickened. 
 09 -  Remove from heat and stir in butter until glossy. Transfer to a bowl, cover surface with plastic wrap, and chill until cold. 
 10 -  Gently fold rainbow sprinkles into chilled pastry cream just before assembly. 
 11 -  Melt white chocolate, heavy cream, and butter together in a heatproof bowl over simmering water, stirring until smooth. Cool slightly. 
 12 -  Slice each choux ring horizontally. Pipe or spoon funfetti pastry cream onto the bottom halves. 
 13 -  Replace tops on filled choux rings. Spoon or drizzle white chocolate glaze over the tops and scatter with extra rainbow sprinkles. 
 14 -  Chill assembled rings for 20 minutes to allow glaze to set before serving.