1. In a small saucepan, combine the half-and-half and the 6 tablespoons butter. Set over medium heat and heat, stirring constantly, until the butter melts and the liquid registers about 125 degrees (52°C) on an instant-read thermometer.
2. To mix by hand: In a large bowl, combine the flour, yeast, sugar, and salt. (If making the poppy seed version, add 1 tablespoon seeds now.) Stir with a wooden spoon until well blended.
3. Check the temperature of the half-and-half mixture; it should now register about 120 degrees (49°C) on an instant-read thermometer. In order for the yeast to grow, the liquid needs to be between 115 and 125 degrees (46 and 52°C). Drizzle the warm liquid over the flour mixture and add the egg yolks. Stir with the wooden spoon until a rough, shaggy dough forms. Lightly dust a work surface with a little flour. Dump the dough onto the surface.
4. Knead the dough with your hands. It will be sticky at first, but resist the urge to add more flour. (If making the Cheddar version, add the cheese and pepper once all the flour is incorporated.) First, gather the dough together. Next, using the heel of one hand, push the top part of the dough away from you. Fold that piece over the dough nearest you. Give the dough a quarter turn clockwise and repeat. Keep on kneading until the dough is smooth and no longer sticky, about 10 minutes. (If making the herb version, add the herbs now and knead briefly to incorporate.) Shape the dough into a ball. Proceed as directed in step 5.
2. To mix in a stand mixer: In the large bowl of a stand mixer, combine the flour, yeast, sugar, and salt. If making the poppy seed version, add 1 tablespoon seeds now. Whisk until well blended.
3. Check the temperature of the half-and-half mixture; it should now register about 120 degrees (49°C) on an instant-read thermometer. In order for the yeast to grow, the liquid needs to be between 115 and 125 degrees (46 and 52°C).
4. Fit the mixer with the dough hook. With the mixer on medium-low speed, slowly pour the warm liquid into the flour mixture. Add the egg yolks. Mix until the flour is completely incorporated. If making the Cheddar cheese version, add the cheese and pepper now. Increase the speed to medium-high and beat until the dough is very smooth and pulls away from the bottom of the bowl (a little will stick to the sides), about 5 minutes. If making the herb version, add the herbs now. If the dough climbs up the hook, stop the mixer and scrape the dough back into the bowl. Don’t venture too far away while the dough is mixing, as the mixer might dance around on the counter because of the large amount of dough. Proceed as directed in step 5.
5. Let the dough rise: Scoop up the dough and shape it into a ball. Lightly grease the bowl and pop the dough back into it. Cover the top securely with plastic. (I like to use a large rubberband to hold the plastic in place.) Let the covered dough rise in a warm spot until doubled in size, 45 to 55 minutes.
6. Lightly grease a 9-by-13-inch (22.75-by-33cm) baking dish (I use Pyrex). Turn the dough out onto a clean work surface and press down gently to deflate. There’s no need to flour the work surface or your hands unless you’re making the herb variation, in which case the dough may be sticky. Using a bench scraper or a chef’s knife, divide the dough into 16 equal pieces, 2 to 2 1/3 (57 to 71 grams) each. (To be sure of uniform rolls, use a scale to weigh the portions.)
7. Work with one piece of dough at a time, and keep the others covered with plastic wrap or a damp towel. Again, there’s no need to flour your hands unless you’re making the herb variation. With a cupped palm, press down gently but firmly, rolling the piece in tight circles on the work surface until it forms a smooth-skinned ball with a seam on the bottom. Put the ball, seam side down, in the prepared baking dish, cover loosely with plastic, and repeat with the remaining dough. The dough balls can be arranged in rows or placed randomly; just be sure they’re evenly spaced.
8. Cover the baking dish with plastic wrap and let the balls rise in a warm spot until they’re about 1 ½ times their original size and have risen about three-fourths of the way up the sides of the baking dish (they won’t yet fill the dish), 40 to 60 minutes.
9. Position an oven rack on the middle rung. Heat the oven to 375 degrees (190°C). If making the poppy seed version, sprinkle the rolls with the 1 teaspoon of poppy seeds now.
10. Bake until the rolls are puffed and well browned, 20 to 25 minutes. Remove from the oven and brush the tops with the melted butter, if using. Serve warm.