Warm the milk and prep the yeast. Heat milk until warm to the touch (about 110°F/43°C). In a large bowl, whisk the warm milk with 2 tablespoons granulated sugar and the yeast. Let it sit for 5–10 minutes until foamy. If it doesn’t foam, your yeast may be inactive.

Make the dough. Add melted (cooled) butter, egg, vanilla, and salt to the yeast mixture. Stir in 3 1/2 cups of flour. Mix until a shaggy dough forms. Add more flour, a few tablespoons at a time, until the dough is soft and slightly tacky but not sticky.

Knead. Knead by hand on a lightly floured surface or with a stand mixer and dough hook for 6–8 minutes. The dough should be smooth and elastic, springing back when poked. Avoid adding too much flour, or the rolls will be dense.

First rise. Place the dough in a lightly greased bowl, cover, and let rise in a warm spot until doubled, 60–90 minutes. A slightly warm oven (turned off) works well.

Prepare the blueberry filling. In a bowl, toss blueberries with 2 tablespoons granulated sugar, 1 tablespoon brown sugar, 1–2 teaspoons cornstarch, and 1 teaspoon lemon zest if using. Set aside. The cornstarch helps thicken the juices.

Make the cinnamon-sugar spread. In a small bowl, mix 1/2 cup brown sugar, 2 teaspoons cinnamon, and a pinch of salt. In another bowl, soften 4 tablespoons butter until spreadable.

Roll out the dough. Punch down the risen dough and roll it into a rectangle about 12x16 inches. Spread the softened butter evenly over the surface. Sprinkle the cinnamon-sugar mixture on top, then evenly scatter the blueberries.

Roll and slice. Starting from the long side, roll the dough into a tight log. Use a sharp knife or unflavored dental floss to slice into 12 even pieces. If the berries try to escape, gently tuck them back in.

Second rise. Arrange rolls in a greased 9x13-inch pan or two round pans with a little space between each. Cover and let rise until puffy, 30–45 minutes. They should expand and nearly touch.

Bake. Preheat oven to 350°F (175°C). Bake for 22–28 minutes, until the tops are lightly golden and the centers are set. If browning too fast, tent loosely with foil for the last 5 minutes.

Make the glaze. Beat 4 ounces cream cheese (softened) with 1 tablespoon melted butter, 1 teaspoon vanilla, 1 cup powdered sugar, and 1–2 tablespoons milk until smooth. For a lighter glaze, skip the cream cheese and mix powdered sugar, milk, vanilla, and a touch of lemon zest.

Glaze and serve. Let the rolls cool for 10 minutes, then spread with glaze. Serve warm for maximum fluffiness and gooey goodness.