Heat the milk in a medium pot over low heat until it reaches 100°F. Remove from heat and add the yeast and 1/2 teaspoon sugar. Give it a quick stir. Let sit until foamy, about 5–10 minutes. (If the mixture doesn’t foam, you may need new yeast, or too-hot milk could have killed the yeast. Start over or the rolls won’t rise).
While the yeast is proofing, melt the butter and let it return to room temperature. Once cooled, whisk in vanilla extract and egg yolk until smooth. Pour this mixture into the base of a stand mixer along with the remaining 1/3 cup sugar. Pour the activated yeast and milk mixture into the bowl of the stand mixer. Mix everything until combined. Add flour and salt on top.
Mix on low speed with the dough hook until thick and slightly sticky (~2 minutes), scraping the sides with a spatula as needed. Knead on medium speed until the dough gathers around the hook, (~5–6 minutes). If the dough is not gathering around the hook, you can slowly add additional flour (1/4 cup up to 3/4 cup extra). You want the dough to be slightly sticky and tacky. Resist the urge to add too much additional flour, as this will take away from the softness of the dough, but the dough should gather around the dough hook and not stick to your fingers.
Remove the dough and shape it into a ball (it will be a little sticky!). Grease the mixing bowl with cooking spray or butter and return the dough to the bowl, turning to coat with the spray or butter. Cover with plastic wrap or a towel and let rise until doubled. This takes roughly 45 mins to 1 hour 15 minutes. Placing the dough in a warm (but not too warm) environment will make it rise a bit faster.
Lightly flour a clean surface and roll out the dough. Try to get a rectangle shape that is approximately 15 x 12 inches (with the 15-inch side facing you). Avoid overworking the dough.
For the Filling
With a table knife, spread the butter evenly over the dough (leaving a 1-inch border on the dough). In a small bowl, combine sugar and lemon zest of 1 lemon (about 1 tablespoon). Rub together with your fingers until fragrant and zest is broken down. Add 1/2 tablespoon lemon juice and mix. Sprinkle this lemon sugar over the butter. Sprinkle and gently press the blueberries evenly over the lemon sugar mixture.
Using a very sharp knife (I use a bread knife), cut the roll of dough into 12 equal slices and place (cut side up) in a well-greased 9x13-inch ceramic or glass pan (avoid metal pans if possible; metal pans will sometimes make the sweet rolls taste metallic and react with the acid).
Preheat oven to 375°F. Cover the rolls in the pan and allow them to rise until nearly doubled, about 20–30 minutes.
Warm the heavy cream for 15–20 seconds in the microwave (not hot, just not cold/straight from the fridge).
Using a pastry brush, brush the heavy cream over the risen rolls and allow it to soak in and around the rolls.
Bake sweet rolls at 375°F for 30–35 minutes, until rolls are lightly golden brown at the edges and the centers are cooked through.
For the Frosting/Glaze
While the rolls are cooling, prepare the glaze. Whisk together the lemon zest of a lemon (about 1 tablespoon), 3 tablespoons lemon juice, melted butter, powdered sugar, and salt.
Allow sweet rolls to cool at room temperature for 5–10 minutes, then spread the glaze evenly over the rolls. Enjoy warm!
Video
Notes
Storage: Store leftovers in a sealed container for 1–2 days or in the fridge for 5 days. Freeze unglazed rolls in a sealed container or wrapped in plastic and foil for up to 2 months. Thaw in the fridge overnight, then warm and glaze.