In a large mixing bowl, combine the yeast, warmed milk (very warm, but not hot to the touch), and 1/2 cup granulated sugar. Set aside to bloom for 5 minutes until frothy.
Add the eggs, melted butter, vanilla extract, and 1 tablespoon lemon zest and mix until well combined. Mix in 4 cups of the flour and salt (this is best done with an electric stand mixer), then knead the dough until smooth, about 5 minutes, adding more flour 1 tablespoon at a time as needed.
Place the dough in a well greased bowl, cover with a clean kitchen towel, and set aside in a warm place to rise until doubled, about 1 hour.
Turn the dough out onto a well floured surface and roll out into a 14x9-inch rectangle. Spread the softened butter over the dough rectangle, then sprinkle with the 3/4 cup of sugar, 1 tablespoon lemon zest, and 1/4 teaspoon salt.
Starting at one of the short ends, roll the dough up like a jelly roll. Use a sharp knife to cut the log into 8 equal rolls. Place the rolls in a greased 9x13-inch glass baking dish. Cover with a clean kitchen towel and set aside in a warm place to rise until risen, about 1 hour.
While the rolls are rising, preheat the oven to 350F. Bake the rolls for 30 minutes until golden brown.
While the rolls are baking, use an electric mixer to beat together the cream cheese and butter for the frosting. Add the powdered sugar, milk, and lemon zest and mix well. Spread the frosting over the hot rolls when they are finished baking. Cool slightly before serving.