In a small bowl or measuring cup, combine warm water with yeast and 1 teaspoon of sugar. Let stand 10 minutes, or until frothy. Meanwhile, in a microwave safe bowl combine milk, butter and remaining tablespoon of sugar. Microwave on high heat for 1 minute, stir, then heat for 30 seconds more. (Milk should be warm, but not hot).
In a large bowl, whisk together flour and salt. Add yeast mixture and milk mixture, stirring until shaggy dough forms. Transfer dough to a clean, lightly floured surface and knead for 10 minutes, or until dough is smooth and elastic. (You can alternatively knead in a standing mixer, using the dough hook, for about 8 minutes). Place dough in an oiled bowl, turning once to coat; cover and let rise 1 hour, or until doubled in volume.
Punch down dough and divide into 12 even portions. Form each portion into a ball, by pulling surface of dough to the underside, pinching the bottoms to secure. Place on greased baking sheets and let rise 30 minutes. Meanwhile, preheat the oven to 400ºF, with two oven racks in the centre positions.
Whisk egg yolk with 1 tablespoon of water, and brush onto tops of rolls. Sprinkle rolls evenly with sesame seeds. Bake 15 to 20 minutes, rotating pans half‐way through, until golden brown and buns sound hollow when tapped on the bottom. Transfer immediately to wire racks to cool.