In a medium saucepan, bring 1¼ cups cream and vanilla bean seeds to a boil.
Meanwhile, in a medium bowl, whisk together egg yolks, sugar, and cornstarch.
When cream begins to come to a boil, pour over egg yolk mixture, whisking constantly until smooth. Return mixture to saucepan, and cook over low heat, whisking constantly until bubbling and very thick. Whisk in butter. Cover with plastic wrap, pressing wrap directly onto surface of custard, and refrigerate until chilled, about 2 hours.
In the bowl of a stand mixer fitted with the whisk attachment, beat remaining ¾ cup cream at high speed until stiff peaks form. Fold into custard. Refrigerate until ready to use.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/le-fraisier-french-strawberry-cake/