In your stand mixer bowl, combine the warm milk, sugar, yeast, egg, bread flour, and baking salt. Mix until a shaggy mass forms, then knead on medium speed for 6 to 8 minutes until the dough base begins to smooth out.

Gradually drop the softened unsalted butter piece by piece into the moving mixer. Continue kneading for an additional 4 to 5 minutes until the fat is seamlessly incorporated and the dough turns silky, elastic.

Transfer the smooth dough mass into a lightly greased bowl. Cover securely and allow to proof at room temperature for 1 to 2 hours until it cleanly doubles in volume.

In a small saucepan, preheat the whole milk, in a separate bowl mix eggs, sugar, cornstarch, and vanilla bean paste until completely lump-free, then combine with warm milk. Place over medium heat and whisk constantly until the mixture thickens into a heavy, smooth pastry cream. Transfer to a clean bowl, press plastic wrap directly onto the custard surface, and let cool completely.

In a separate small saucepan, combine the smooth strawberry juice or puree with sugar. Bring to a gentle simmer and cook for 2 to 3 minutes until slightly thickened. Set aside to cool. Toss your small fresh strawberries directly into this glaze right before assembly.

In a small bowl, mix the all-purpose flour, sugar, and baking salt. Pour in the melted butter and toss gently with a fork until standard crumbly streusel pebbles form; set aside.

Deflate your double-risen dough gently. Tip onto a clean surface and divide into 8 to 9 equal portions weighing roughly 85–90g each. Roll each portion firmly into a tight, smooth ball.

Arrange the rounded dough balls neatly onto a baking sheet lined with parchment paper, leaving generous space between each. Cover loosely and allow them to proof for 45 to 60 minutes until noticeably puffy and nearly doubled.

Preheat your home oven to 325°F (165°C). Uncover the puffy dough balls and brush their outer surfaces lightly with beaten egg wash.

Lightly grease the flat bottom of a drinking glass or the back of a large spoon. Press it firmly straight down into the exact center of each proofed ball to form a deep, wide cavity.

Spoon a generous portion of the cooled vanilla custard directly into each stamped cavity. Arrange the glazed strawberries neatly over the custard core, then scatter a heavy layer of the fork-crumbled streusel pebbles across the top of the fruit.

Slide the pan onto the middle oven rack and bake at 325°F (165°C) for 25 to 27 minutes. The buns are done when the outer dough rings turn a soft, light golden brown and the core custard is set. Cool on the baking tray for 10 minutes before sliding onto a wire rack. Serve warm or at room temperature.