In a small saucepan, whisk together the flour and milk until smooth. Cook over medium heat, whisking constantly, until thickened into a paste that leaves visible lines when stirred, about 2–4 minutes. Transfer to a bowl and let cool to room temperature.

In a small bowl, whisk the warm milk and sugar until dissolved. Sprinkle the yeast over the top and let sit for 5 minutes until foamy.

In the bowl of a stand mixer fitted with the dough hook, combine the cooled tangzhong, yeast mixture, melted butter, eggs, lemon zest, vanilla, lemon extract (if using), salt, and both flours. Mix on low speed until a soft dough forms.

Knead on medium speed for 5–8 minutes until smooth and elastic. Add the softened butter one tablespoon at a time until fully incorporated. The dough will be soft and slightly sticky.

Transfer to a greased bowl, cover, and let rise in a warm place for 1–2 hours, until doubled.

For easier shaping, refrigerate the dough for 2–8 hours or overnight after the first rise.

In a small bowl, mix together the sugar, lemon zest, and salt with your fingers to release all of the lemon zest oils.

Grease a 9×13-inch baking pan.

Roll the chilled dough into a 16×12-inch rectangle with the long side facing you. Spread softened butter on there, sprinkle with the lemon sugar evenly over the dough, leaving a ½-inch border along the far long edge.

Dollop the lemon curd evenly over the filling in small spoonfuls. Gently smear once or twice with an offset spatula to create pockets of curd.

Roll the dough tightly from the long side and slice into 12 rolls using a sharp knife or dental floss. Arrange in the prepared pan.

Cover loosely and let rise for 45–60 minutes, until puffy.

Preheat the oven to 325°F and bake for 28–32 minutes, until set and lightly golden on top. Tent loosely with foil if browning too quickly.

Let the rolls cool for about 10 minutes before frosting.

Beat the cream cheese and butter together until smooth. Add powdered sugar, vanilla, lemon zest, lemon extract, and salt, and mix until creamy and spreadable.

Spread over warm (not hot) rolls. Decorate with a light swoop of lemon curd if you'd like.