Warm 1 cup of buttermilk until it reaches 100–110°F, stir in 1/4 cup of granulated sugar and sprinkle 2 1/4 teaspoons of dry active yeast on top. Let foam for about 5 minutes.

Combine the yeast mixture with 1 large egg, 1 egg yolk, 1/4 cup melted unsalted butter, 1/2 teaspoon kosher salt, 3 1/2 cups all-purpose flour, and the zest of 1 lemon until a sticky dough forms.

Transfer the dough onto a floured surface and knead for about 5–7 minutes until smooth and elastic. Put into a lightly greased bowl and let rise for 1 hour until doubled in size.

In a saucepan over medium heat, combine 2 cups of blueberries, the juice of 1 lemon, and 1/4 cup of granulated sugar. Stir in 1 tablespoon of cornstarch and cook for about 5 minutes to thicken.

Mix together 1/4 cup softened unsalted butter, 1/2 cup light brown sugar, and 1 tablespoon ground cinnamon in a bowl until smooth.

Punch down the dough, roll it onto a floured surface into a rectangle, spread the cinnamon mixture, followed by the cooled blueberry filling. Roll into a log and cut into 12 equal pieces.

Arrange the sliced rolls in a buttered 9x13 inch baking dish and let rise for another 20 minutes.

Preheat oven to 375°F and bake the rolls for 20–25 minutes until golden brown and bubbly.

Whisk together 1 cup powdered sugar, 2 tablespoons lemon juice, and zest of 1 lemon until smooth. Drizzle over warm rolls after baking.