1. For tangzhong, in a small saucepan, whisk together water and whole milk; whisk in flour. Cook and whisk constantly over medium-low heat for 5 to 7 minutes or until mixture thickens enough to coat the back of a spoon and leaves a line when your finger is drawn across the spoon. Transfer tangzhong to a large mixing bowl for a stand mixer; cool to room temperature.
2. For the dough, in another large bowl, whisk together flour, milk powder, sugar, yeast and salt; set aside.
3. Add whole milk, melted butter and eggs to bowl with cooled tangzhong. Use a silicone spatula to stir until combined; add half of the flour mixture. Attach dough hook to stand mixer. Beat on medium until nearly all of the flour is incorporated, stopping occasionally to scrape side of bowl. Add remaining flour mixture. Beat on medium for 9 to 10 minutes or until mixture forms a soft, smooth dough. The dough will be extremely sticky.
4. Turn dough out onto a lightly floured surface. Gently knead 10 to 12 times. Lightly spray a large, clean bowl with nonstick cooking spray; transfer dough to bowl. Spray one side of plastic wrap with cooking spray; cover dough loosely with plastic wrap and a kitchen towel. Let rise in a warm place (80°F to 85°F) about 1 hour or until double in size.
5. Meanwhile for the filling, in a small bowl combine brown sugar, cinnamon and cardamom; set aside. Grease a 13×9-inch baking pan with remaining 1 tablespoon butter; set aside.
6. Gently push fist into dough. Transfer dough to a lightly floured surface. Roll dough into a 24×13-inch rectangle. Sprinkle filling over dough; lightly pat filling into an even layer.
7. Starting from one of the long sides, tightly roll dough with filling into a log. Trim and discard uneven ends. Using dental floss, cut log into 12 (2-inch-thick) rolls. Arrange rolls in prepared baking dish. Cover rolls loosely with a clean kitchen towel. Let rise in a warm place (80°F to 85°F) about 30 minutes or until slightly puffy.
8. Place oven rack in center of oven; preheat oven to 350°F. Uncover rolls and bake for 25 to 30 minutes or until golden brown. Cool for 10 minutes in baking pan on wire rack.
9. For frosting, in a bowl for a stand mixer, fitted with a paddle attachment, beat cream cheese and butter on medium until fluffy. Add powdered sugar and salt. Beat on low just until combined; beat on medium for 30 to 60 seconds until smooth and creamy. Spread frosting onto warm rolls.

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To make ahead: Completely cool rolls in baking pan. Do not spread with frosting. Tightly wrap rolls in baking pan with heavy foil. Freeze up to 1 month. To reheat, loosely cover baking pan with frozen rolls with foil. Heat in a 250°F oven about 1½ hours or just until thawed and warmed through. Spread with frosting. Serve warm.

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