Stir together butter, sugar, lemon zest, salt and flour until it forms a paste.
Once the dough is risen, roll it out on a lightly floured surface into a large rectangle, about 10” by 14”. Spread the filling as evenly as possible over the rectangle, making sure to reach to the sides so the outer rolls have enough filling. Sprinkle with blueberries. I used 1 cup of mini (or “wild”) blueberries that were defrosted and drained. If you’re using regular sized berries, you might want to use more of them.
Roll the dough up tightly from the long end. Slice it into 12 equal rounds. Place the rolls into a 9x13” pan that has been sprayed with cooking spray.
Cover the rolls with plastic wrap and refrigerate overnight. (Or, if you want to make them the same day, cover with plastic wrap and let them sit for 1 hour until they’ve puffed up a little, then continue as directed below.)
When ready to bake, preheat oven to 350°F. Remove the rolls from the refrigerator and let them warm up to room temperature while the oven is preheating. Remove the plastic wrap and bake for 23-28 minutes, or until they are golden brown. (Mine took 24, be careful not to over bake. The bottoms will turn golden before the tops do.) Note: the blueberries will drain to the bottom of the pan overnight. That’s not a problem.