In a large bowl, combine warm milk, yeast, and 1 tablespoon of sugar. Let sit for 5–7 minutes until foamy.

Add eggs, remaining sugar, salt, and flour. Mix until a soft dough forms.

Knead the dough for 8–10 minutes, gradually incorporating the softened butter until smooth and elastic.

Cover and let rise in a warm place for 1–1.5 hours, or until doubled in size.

In a small bowl, gently toss blueberries with brown sugar, cornstarch, vanilla, and lemon zest.

Roll the dough into a rectangle, spread the blueberry mixture evenly, and roll tightly into a log.

Slice into even buns and place in a greased baking dish. Cover and let rise for 30 minutes.

Preheat oven to 350°F (175°C). Brush buns with egg wash.

Bake for 25–30 minutes until golden brown and fragrant.