For the dough, stir together the milk, yeast, and ½ teaspoon of the sugar; set aside for 10 minutes or until foamy.
Put the butter, salt, egg, lemon zest, lemon juice, and the remaining ⅓ C. sugar into the bowl of a stand mixer fitted with a paddle attachment. Mix until the butter is evenly distributed, but still a bit chunky. Add the yeast mixture and beat for a few seconds more. Gradually add 3 cups of the flour, mixing until the dough just just begins to stick to the paddle.
Replace the paddle with a dough hook and continue mixing on low speed until the dough forms a ball. The dough should be elastic with minimal transfer to your finger when touched. If it's too wet, beat in up to ¼ cup flour, a little at a time.
Spray a big bowl with cooking spray, add the dough, and spray the top of the dough. Cover the bowl with plastic wrap and set aside until double in size.
For the filling, stir together the butter, sugar, lemon zest, flour, and salt. Roll out the risen dough on a lightly floured surface to a 10 x 14" rectangle; spread the filling evenly over the dough and sprinkle with the blueberries.
Roll up the dough tightly, starting from a long end. Slice into 12 equal rounds and arrange in a greased 9 x 13" baking pan. Cover with plastic wrap and set aside for an hour or until they're a little puffy (they can also be refrigerated overnight then brought to room temperature before baking).
Preheat the oven to 350°. Uncover the rolls and bake for 25 minutes or until golden brown; don't overbake.
For the frosting, stir together the butter, cream cheese, powdered sugar, salt, and lemon juice until smooth. Spread over the rolls and enjoy.