Rub lemon zest into sugar in a small bowl to release natural oils
Mix softened butter and vanilla into the sugar mixture until smooth and set aside
Whisk cream cheese, butter, and vanilla together
Add powdered sugar and salt to the cream cheese mixture
Whisk in lemon juice, zest, and poppy seeds until smooth and creamy, then refrigerate
Add yeast, sugar, milk, heavy cream, crème fraîche, egg, butter, lemon zest, and vanilla to stand mixer bowl and whisk to combine
Add remaining dry ingredients and mix on medium with dough hook until well combined
Continue mixing for 5 minutes until cohesive dough forms, adding 1 tbsp flour at a time if sticky
Allow dough to rise in warm place until doubled in size (1-2 hours)
Punch down dough and roll out onto floured surface into a 12-inch wide rectangle
Evenly spread filling and tightly roll dough lengthwise to form a log
Cut log into 6 even pieces using sharp knife or string
Place rolls on parchment-lined sheet pan and let rise for 30 minutes
Drizzle heavy cream onto each roll and bake at 350°F for 28-32 minutes
Frost rolls while warm and serve
