01 - Preheat oven to 200°F. In a large mixing bowl or stand mixer, combine all-purpose flour, instant dry yeast, poppy seeds, and fine salt.
02 - In a separate bowl, combine buttermilk, granulated sugar, and unsalted butter (cut in pieces). Microwave for 1 minute until just warm, then stir until smooth.
03 - Gradually pour the warm buttermilk mixture into the dry ingredients and mix with a dough hook on medium speed, or by hand. Dough will be sticky.
04 - Mix in eggs one at a time until a sticky dough forms. Continue mixing until dough is elastic, then add lemon zest and mix until fully incorporated.
05 - Add extra flour one tablespoon at a time until dough pulls away from bowl sides, feeling tacky but not sticky. Cover and let rest 10–20 minutes.
06 - In a medium bowl, combine granulated sugar, brown sugar, and lemon zest. Massage zest into sugars, then add softened butter and whisk until smooth.
07 - Roll out dough on a floured surface to a 12 x 18-inch rectangle, about 1/4-inch thick. Evenly spread filling over dough, leaving a 1/2-inch border.
08 - Tightly roll dough from the long edge. Using dental floss, cut roll into 12 equal segments. Arrange evenly in a greased or lined 9 x 13-inch baking pan.
09 - Turn off the oven, cover rolls with foil, and place inside to rise for 30 minutes.
10 - Remove rolls; preheat oven to 350°F. Return pan and bake 28–32 minutes until golden brown.
11 - While rolls cool, whisk powdered sugar, fresh lemon juice, and melted butter in a bowl until smooth.
12 - Spoon icing over warm rolls after 10–20 minutes of cooling; garnish with fresh lemon zest before serving.