Step 1

Whisk ¾ cup whole milk and ¼ cup (31 g) all-purpose flour in a medium saucepan until smooth. Place saucepan over medium heat and cook, whisking constantly, until mixture is thickened and whisk lines are visible on bottom of pan, about 2 minutes. Scrape tangzhong into the bowl of a stand mixer and let cool.

Step 2

Add 1 large egg, one ¼-oz. envelope instant yeast (about 2¼ tsp.), ⅓ cup (67 g) granulated sugar, 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt,  and remaining 1½ cups whole milk to tangzhong and whisk to combine. Add remaining 5½ cups (688 g) all-purpose flour. Fit bowl onto stand mixer; fit mixer with dough hook attachment. Mix on low speed until combined, about 1 minute. Increase speed to medium-low and mix, scraping down sides of bowl occasionally, until dough is smooth and elastic, 18–24 minutes. Pinch off a golf-ball-size piece of dough and stretch between your fingers as thin as possible without breaking. If you can see light through the dough, it’s ready. If not, continue mixing a few more minutes, then try again.

Step 3

Add ½ cup (1 stick) unsalted butter, room temperature, cut into pieces, to dough and mix on medium speed until incorporated, about 2 minutes. Continue mixing until dough pulls away cleanly from sides of bowl and is no longer tacky to the touch, 5–7 minutes longer. Remove bowl from mixer and cover with a damp kitchen towel. Let sit in a warm spot until doubled in volume, 60–90 minutes.

Step 4

While the dough is rising, cook ½ cup (1 stick) unsalted butter in a small saucepan over medium heat, stirring occasionally, until butter foams and milk solids turn dark amber, about 4 minutes. Transfer to a heatproof bowl and let cool slightly. Add 1 cup (packed; 200 g) dark brown sugar, 2 Tbsp. ground cinnamon, 2 Tbsp. heavy cream, and ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt to butter and mix to combine.

Step 5

Butter two 9"-diameter cake pans. Punch down dough and transfer to a lightly floured surface. Stretch dough into a rough rectangle; if dough feels stiff, let sit 5–10 minutes to allow gluten to relax. Arrange dough with short side facing you and roll out to a 24x13" rectangle. Spread filling over dough in an even layer.

Step 6

Starting at edge closest to you, tightly roll up dough into a log; roll log seam side down. Using a sharp serrated knife and long sawing motions, trim ends of log; discard. Using serrated knife or, preferably, unflavored dental floss, cut log in half crosswise, then cut each half into 6 equal rounds. (If using dental floss, slide floss underneath dough, then cross over top and pull ends through.) Nestle 6 rounds, cut side down, in each prepared cake pan. Cover with damp kitchen towels and let sit in a warm spot until doubled in volume, about 30–50 minutes.

Step 7

Place a rack in middle of oven; preheat to 350°. Bake rolls until golden on top and puffed (don’t be alarmed if they rise dramatically in the center), 25–30 minutes.

Step 8

Meanwhile, using an electric mixer on medium speed or a whisk, beat 4 Tbsp. unsalted butter, room temperature, and 8 oz. cream cheese, room temperature, in a large bowl, scraping down sides of bowl as needed, until combined. Add 1¼ cups (138 g) powdered sugar, 1 Tbsp. heavy cream, 1 tsp. lemon zest (if using), and ¼ tsp. Diamond Crystal or Morton kosher salt and beat until mixture is smooth and sugar is incorporated. Taste and beat in more powdered sugar (up to ¾ cup) if desired. Thin with more cream as needed, a teaspoonful at a time, until frosting is thick but spreadable.

Step 9

Let cinnamon rolls cool in pan 5 minutes; spread frosting over.