Heat cream, sugar, vanilla, and half of milk until boiling; whisk cornstarch, egg yolk, and remaining milk, then combine and cook until thickened. Cool completely.
Warm milk to 38°C, add yeast and sugar; let foam. Mix with flour, remaining sugar, egg, butter, and salt; knead into a smooth dough. Let rise 90 minutes.
Prepare streusel by mixing butter, sugar, flour, vanilla, and salt; chill until use.
Divide risen dough into 12 balls, rest 20 minutes. Shape each into a bowl, fill with pudding and jam, then top with streusel. Bake at 180°C for 55 minutes until golden.
Notes
Ensure the dough is kneaded well for a soft texture and chill the streusel for better crumbly topping.