Pour warm water into a medium bowl. Add 1 teaspoon of sugar and the yeast, whisk to dissolve. Let sit for 8-10 minutes until thick foam forms on top.

Sift the flour into a large bowl. Make a well in the middle and add sugar, salt, warm milk, eggs, softened butter, vanilla extract, lemon zest, and the bloomed yeast mixture.

Whisk the ingredients in the middle of the well together, then slowly incorporate the flour into the wet mixture. Keep mixing until it forms a shaggy, sticky dough. Cover and let rise in a warm place for 45-55 minutes until puffed and doubled in size.

Deflate the dough by lifting one edge over the rest, repeating 6 times until smooth.

Transfer the dough onto a floured surface and roll it out into a large rectangle.

In a separate bowl, whisk together the lemon curd and cornstarch. Spread the mixture on top of the dough.

Starting with the longer edge, roll the dough into a tight roll. Cut into 12 equal pieces using unflavored floss or thin cotton string.

Place each roll in a buttered 8" by 12" rectangular baking pan. Let rise for about 15 minutes.

Preheat the oven to 355?F (180?C). Pour heavy cream over the rolls and bake for 25-30 minutes until golden brown.

For the frosting, beat softened butter until light and fluffy. Add powdered sugar and salt, then beat until fluffy.

Add sour cream, vanilla extract, and lemon juice. Beat well until very light and fluffy.

Spread the frosting onto the warm rolls and add dollops of lemon curd, swirling them together.