In a mixing bowl, combine the bread flour, sourdough starter, water, salt, and sugar. Mix until a shaggy dough forms.

Knead the dough for about 10 minutes until smooth and elastic. Place in a lightly greased bowl, cover, and let rise for 2 hours or until doubled in size.

In a separate bowl, combine the chopped strawberries, sugar, and vanilla extract. Let sit for 15 minutes to macerate.

Once the dough has risen, turn it out onto a floured surface. Roll it into a rectangle about 1/2 inch thick.

Spread the macerated strawberries evenly over the dough. Roll the dough tightly into a log and cut into 12 equal pieces.

Place the rolls on a baking sheet lined with parchment paper. Cover and let rise for another hour.

Preheat the oven to 375°F (190°C). Brush the tops of the rolls with the beaten egg and sprinkle with sugar.

Bake for 20-25 minutes or until golden brown. Let cool slightly before serving.