Prepare the Tangzhong by whisking together the water and 1/4 cup of bread flour in a saucepan. Cook over medium heat, stirring constantly, until thickened into a roux, about 4-5 minutes.

Mix the Lemon Sugar by rubbing the fresh lemon zest into the granulated sugar until it resembles wet sand.

Combine dry ingredients in a stand mixer by whisking together 3 2/3 cups of bread flour, the lemon sugar, instant yeast, and fine sea salt.

Add wet ingredients by pouring in the heavy cream, whole milk, large egg, and the prepared tangzhong. Knead on low speed for about 2 minutes.

Incorporate butter by adding the cool unsalted butter one tablespoon at a time, kneading until the dough is smooth.

Let dough rise by forming it into a ball and placing it seam-side down in a greased bowl. Cover and let rest for 30 minutes.

Prepare the filling by combining cool unsalted butter, light brown sugar, lemon zest, and vanilla until smooth.

Roll out the dough into a 21×15-inch rectangle. Spread the lemon-sugar mixture and lemon curd over the dough.

Cut and shape the rolls by slicing the dough into twelve strips and rolling each into snug spirals.

Allow the rolls to rise again by covering the pan and letting it sit for 1-2 hours until doubled in size.

Preheat the oven to 325°F (165°C).

Bake the rolls for 30-35 minutes until light golden brown.

Make the cream cheese frosting by mixing cold cream cheese and unsalted butter, then adding powdered sugar and folding in lemon zest and heavy cream.

Frost and serve the rolls by allowing them to cool slightly, then frosting generously with a dollop of lemon curd.