You need a stand mixer fitted with paddle attachment; a 3-inch round cookie cutter (for burger buns) or 2 (13 x 9 inch) baking pans(for hot dog buns).
Make dough: Bring milk and cream to a bare simmering a small saucepan over medium heat. Cool mixture to 105 to 115 degrees F.
Meanwhile, stir together warm water and yeast in mixer bowl and let stand until foamy, about 5 minutes. (If mixture doesn’t foam, start over with new yeast).
Add warm milk mixture, sugar, flour, and salt to yeast mixture and mix at low speed, scraping down side of bowl as necessary, until flour is incorporated. Increase speed to medium and beat 6 minutes. Dough will be sticky.
Transfer dough to a lightly oiled large bowl and turn to coat with oil. Cover with a kitchen towel (not tery cloth) and let rise in a draft-free place at warm room temperature until doubled, about 2 hours.
To make hamburger buns: Butter 2 large baking sheets. Punch down dough, then roll out on a floured surface with a floured rolling pin into a 14-inch round (about 1/2 inch thick). Cut out as many rounds as possible with floured cutter, arranging 3 inches apart on baking sheets. Gather and re-roll scraps , then cut out more rounds. Loosely cover buns with oiled plastic wrap and let rise in a draft-free place at warm room temperature until they hold a finger mark when pressed gently pressed (1 1/2 to 2 hours).
Preheat oven to 375 degrees with racks with in upper and lower thirds.
Brush buns with some of egg and sprinkle with sesame seeds. Bake, switching position of sheets halfway through, until tops are golden and undersides are golden-rown and sound hollow when tapped, 20 to 25 minutes. Transfer to racks to cool completely.
Tom Make Hot Dog Buns: Butter baking pans. Punch down dough, then divide into 16 equal pieces (about 3 oz each). Roll each pieces of dough into a 6-inch-long log on a lightly floured surface. Space 8 logs evenly in each pan so that there are 2 columns of logs that run parallel to long sides of pan. Loosely cover buns with oiled plastic wrap and let rise in a draft-free place at warm room temperature until buns start to touch 1 1/2 to 2 hours.
Bake buns, switching position of pans halfway through, until tops are golden and undersides are golden-brown and sound hollow when tapped, 20 to 25 minutes, then transfer to racks to cool completely. Before using buns, pull apart and cut lengthwise down center of each (but not all the way through).
Buns are best the day they are made but can be frozen in sealable bags up to 2 weeks.