Grease a half-sheet pan with nonstick spray and set aside.
Place the milk, sugar, yeast, flour, egg yolks, and salt in the bowl of a stand mixer fitted with the paddle attachment. Combine on low speed for 1 minute. Change the paddle attachment to the dough hook and rest the dough for 10 to 15 minutes.
Add 4 tablespoons of the room temperature butter and mix on low speed. Increase the speed to medium and mix until the dough pulls away from the sides of the bowl and you are able to gently pull the dough into a thin sheet that light will pass through, about 8 minutes.
Turn the dough out onto a lightly floured work surface and roll and shape with hands to form a large ball. Return dough to the bowl, cover with plastic wrap, and set aside in a warm, dry place to rise until doubled in size, about 1 hour.
Remove the dough from the bowl and roll into a 16-by-3-inch log. Use a bench knife to cut the dough into 1 3/4-ounce portions, about 16 rolls. Using your loosely cupped hand, roll each portion on the counter until they tighten into small balls. Working 1 at a time, using a rolling pin, or pressing with the palm of your hand, work each small ball into a 3-inch circle or oval. Use the side of your hand or a small dowel to make an indentation across the middle of the circle. Place a cube of the chilled butter into the center of the indentation, then fold in half and gently press to gently seal the edges. Place the rolls, top-side down, onto the prepared sheet pan, spacing them evenly. Melt the remaining 2 tablespoons butter and brush the tops of the rolls. Cover with plastic wrap and set aside in a warm, dry place to rise until doubled in size, 30 to 40 minutes.
When ready to bake, heat the oven to 400ºF.
Remove the plastic wrap and bake until the rolls reach an internal temperature of 200ºF, 8 to 10 minutes. Rotate the pan halfway through baking.
Remove the pan to a wire rack and cool for 2 to 3 minutes before serving.
For Brown and Serve option: Assemble rolls as above. Heat oven to 275ºF. Bake until the outside of the rolls just begin to set but have not browned and the internal temperature is 185ºF, about 30 minutes. Remove and cool on the pan for 10 minutes. After 10 minutes, remove the rolls from the pan and place on a cooling rack until they are room temperature, 30 to 40 minutes. Place the rolls in bags and freeze for up to 3 months.
When ready to bake, heat the oven to 400ºF. Thaw the rolls for 60 to 90 minutes.
Grease a sheet pan with nonstick spray. Place the rolls on the prepared sheet pan and bake until the rolls reach an internal temperature of 200ºF. Rotate the pan halfway through baking, 10 to 12 minutes. Remove the pan to a wire rack and cool for 2 to 3 minutes before serving.