Make the Dough
Warm milk and combine with yeast and 1 tbsp sugar; let sit 5–10 mins until foamy.
Mix remaining sugar, eggs, and melted butter in a large bowl.
Stir in yeast mixture.
Gradually add flour and salt; knead until smooth and elastic (about 5 mins).
Place dough in oiled bowl, cover, and let rise in warm spot until doubled (60–90 mins).
Prepare the Filling
In a saucepan, cook blackberries, brown sugar, cornstarch, and lemon juice over medium heat.
Slightly mash berries and cook until thickened (5–7 mins). Let cool completely.
Assemble the Rolls
Punch down dough and roll into 16x12 inch rectangle.
Spread softened butter, then cooled filling.
Roll up tightly and cut into 12 even rolls.
Place in greased baking dish, cover, and rise again 30–45 mins.
Bake and Glaze
Preheat oven to 350°F.
Bake 25–30 mins until golden and hollow-sounding when tapped.
Mix glaze ingredients; drizzle over slightly cooled rolls.