• Add the warm milk to the bowl of a stand mixer. Sprinkle yeast and sugar over the milk. 
• If using active dry yeast, let this sit for around 5-10 minutes until it becomes foamy; if using instant yeast, this step can be skipped.
• Add the flour, salt, eggs, sour cream and chives to the yeast mixture. Fit the stand mixer with a dough hook attachment and mix on low speed until a thick dough forms.
• Add in the softened butter, a few cubes at a time. Keep mixing on medium speed for around 15 minutes until the dough is soft and strong and pulls cleanly away from the sides of the bowl. This might take longer depending on your mixer. All the fat in the sour cream and butter inhibits gluten formation, so you’ve got to give the mixing enough time.
• Once kneaded, form the dough into a smooth ball. Transfer the dough to a lightly greased large bowl and cover it with plastic wrap or a damp dish towel.
• Let the dough rise in a warm place until doubled in size, around 1 to 1 ½ hours. A warm room temperature will speed up the rising time. You can also let the dough rise in the refrigerator, for up to 16 hours.

Shaping

• Grease or line a 9x13-inch baking dish with parchment paper.
• Punch down the risen dough, then pull it from the bowl onto a lightly floured work surface. Dust the top of the dough with some flour.
• Use a kitchen scale to measure the weight of the whole dough, then divide this by 15 or 20 depending on the size of roll you want.
• Cut the dough into equal pieces with a bench scraper or sharp knife, and use the scales to ensure they are even.
• Shape each piece of dough into a ball and place it the prepared pan.
• Loosely cover the pan and let the dough balls rise in a warm place until doubled in size.

Baking

• Preheat the oven to 350°F (180°C). 
• Bake the rolls for around 30 minutes until deep golden brown. If they are browning too fast, you can cover the top of the rolls loosely with a sheet of aluminum foil. 

  An instant-read thermometer inserted into the center will read about 190°F.
• When the rolls are hot from the oven, brush the tops with butter. Let them cool on a wire rack before serving.