In the bowl of a stand mixer, whisk together the milk, yeast, sugar, egg, egg yolk, salt, and lemon zest until smooth. Attach the dough hook to the stand mixer. Add in half the flour. Mix on slow speed until a dough starts to form.
Continue to mix on low speed adding the softened butter one tablespoon at a time. Add the remaining flour and mix on low speed until incorporated.
Increase the speed to medium and knead until the dough is smooth and cleans the sides of the bowl. Transfer the dough to a lightly greased large bowl. Cover with plastic wrap and let the dough rest for one hour, or until doubled in volume.
PREPARE THE FILLING:
In a medium bowl, use a sturdy rubber spatula to cream together the softened butter, sugar, brown sugar, lemon zest, and salt until smooth. Cover and set aside.
ASSEMBLE:
Punch down the risen dough. Transfer to a lightly floured work surface. Roll the dough into a 20x14-inch rectangle. Spread the filling over the dough.
Starting at the long edge, roll the dough into a tight log. Slice the log into 12 equal parts and place in a greased 9x12-inch baking pan. Cover with plastic wrap and let the rolls rest at room temperature for 30 to 40 minutes. By this time, the rolls should be puffy.
Preheat the oven to 350 degrees F. Remove the plastic wrap and bake the rolls for 30 to 35 minutes, until golden brown on top and the internal temperature of the rolls registers at least 185 degrees F. Allow the rolls to cool for 10 minutes before covering with frosting:
PREPARE THE FROSTING:
In a medium bowl, use an electric mixer to combine the cream cheese and butter until creamy. Add the powdered sugar, lemon juice, lemon zest, and salt. Mix until smooth. Spread over the lemon sweet rolls. If desired, garnish with additional grated lemon zest.
Notes
These are best enjoyed warm or at room temperature the day they are baked.
Dough can be prepared ahead of time and stored in the fridge overnight. Follow steps up to placing cut rolls in greased pan. Cover with plastic wrap and chill in the fridge overnight to slow down yeast. Before baking, allow rolls to sit at room temperature for 45 minutes to an hour to reactivate yeast.
Leftovers can be stored in an airtight container in the fridge for up to three days. Reheat in the microwave or toaster oven to soften bread.
If using active dry yeast: dissolve active dry yeast in warm milk. Let sit for 5-7 minutes until bubbly and fragrant. Then, proceed with instructions as written.