In large mixing bowl or in the bowl of a stand mixer fitted with paddle attachment add egg yolks, whole egg, sugar, 6 tablespoons butter and buttermilk. Mix on low to combine. Replace paddle attachment with dough hook and add flour, yeast and salt. Knead on low speed 5 minutes (alternatively, knead dough on floured surface for 10 minutes). Increase the mixer to medium speed and continue to knead for 5 minutes (5-10 minutes by hand) until dough no longer sticks to sides of bowl or pulls up with the dough hook.

Lightly spray large bowl with cooking spray. Shape dough into ball and place in bowl; turn to coat with oil. Cover bowl with plastic wrap and let rise in warm place 2 to 2 1/2 hours until doubled.

Meanwhile, make filling: In medium bowl, combine brown sugar, cinnamon and salt until well mixed.

Grease bottom and sides of 13x9-inch baking dish with butter. Punch down dough; turn out onto lightly floured surface and gently shape into rectangle, long side facing you. Use rolling pin to roll into approximately 18x12-inch rectangle. Brush 1 1/2 tablespoons melted butter over dough to within 1/2-inch of top long edge. Sprinkle filling mixture over dough, then gently press into dough.

Beginning with long end nearest you, carefully roll dough into tight log. Firmly pinch seam to seal and turn so seam side is down. Using serrated knife, cut dough into 12 equal-size rolls (about 1 1/2 inches each). Arrange cut side-down in prepared baking dish. Cover tightly with plastic wrap and refrigerate overnight (8 hours) up to 16 hours.

When ready to bake, remove rolls from refrigerator and place in oven that is turned off. Place shallow pan on rack just beneath rolls; add enough boiling water to pan to fill 2/3-full. Immediately close oven door and let rolls steam 30 minutes until puffy. Remove rolls and shallow pan from oven.

Heat oven to 350 degrees F. Return rolls to oven and bake 30 to 35 minutes until deep golden brown.

While rolls are cooling, make frosting: In medium bowl, beat cream cheese, butter, vanilla and powdered sugar with electric hand mixer or in bowl of stand mixer until smooth and creamy. Spread over warm rolls and serve immediately.