Whisk buttermilk and butter together in a large liquid measuring cup. Combine 3 1/2 cups flour, lemon zest, sugar, yeast, and salt in a stand mixer fitted with dough hook. With the mixer on low, add buttermilk mixture and eggs, and mix until dough comes together, about 2 minutes. Increase speed to medium; if the dough is still very sticky and hasn't cleared the sides of the bowl yet, add a little flour at a time until dough has pulled away from sides of the bowl but is still slightly sticky. Knead dough until it is smooth and elastic, about 5-6 minutes (10 minutes by hand). Don't over flour the dough or the rolls may be dry. Place dough in a large, lightly greased bowl and cover top tightly with greased plastic wrap. Let dough rise in a warm place until doubled, 1-2 hours. Lightly grease a 9x13 baking dish and set aside.

Lemon Filling: Combine sugar and lemon zest and rub between fingers until well combined and fragrant. Add the nutmeg and lemon juice and stir until combined.

When the dough has risen, turn it out onto a lightly greased counter and press into a 16x12 rectangle. Spread butter evenly over dough. Sprinkle Lemon Filling over top and spread evenly to edges. Starting with one long end, tightly roll up the dough cinnamon-roll style and pinch seam to seal. Cut dough into 12 equal pieces and place in prepared pan, 3 across, 4 down. Cover with greased plastic wrap and let rise until doubled. Preheat oven to 350 F. Uncover and bake 20-25 minutes until very lightly golden. Cool slightly before frosting.

Lemon Cream Cheese Glaze: Whip cream cheese and lemon juice together with an electric mixer until smooth and creamy. Add powdered sugar and mix until well-combined. Spread Glaze evenly over buns and sprinkle with fresh lemon zest.