Whisk the water and flour together in a saucepan over medium heat. Stir constantly until the mixture thickens into a paste-like roux, about 4–5 minutes. Transfer to a bowl and let cool.

Rub the lemon zest into the granulated sugar using your fingertips until fragrant and sandy.

In a stand mixer bowl, whisk together the bread flour, lemon sugar, yeast, and salt. Add the heavy cream, milk, egg, and cooled tangzhong.

Knead with a dough hook on low speed for 2 minutes until a rough dough forms.

With the mixer running on low, add the butter one tablespoon at a time, allowing each piece to fully incorporate. Continue kneading for about 12 minutes until the dough becomes smooth and elastic.

Shape the dough into a smooth ball and place it into a lightly greased bowl. Cover and let rest for 30 minutes.

Mix together the butter, brown sugar, lemon zest, and vanilla until smooth.

Roll the dough into a 21×15-inch rectangle on a lightly floured surface. Spread the lemon sugar filling evenly over the dough, leaving a 1-inch border at the top. Spread the lemon curd over the filling.

Using a pizza cutter, cut the dough into 12 strips. Roll each strip tightly and place into a parchment-lined 9×13 baking pan.

Cover the pan and let the Lemon Sweet Rolls rise for 1–2 hours or until doubled in size. Preheat the oven to 325°F (162°C).

Bake for 30–35 minutes until lightly golden on top.

Beat together the cream cheese and butter until smooth. Add powdered sugar and continue mixing until fluffy. Mix in the lemon zest and heavy cream.

Cool the rolls for 15 minutes before spreading the frosting over the top. Add extra lemon curd and serve warm.