for the burgers

1. Prepare a charcoal or gas grill for direct grilling over medium-high heat.
2. In a large bowl, mix together the beef, yellow onion, garlic, salt, pepper and Worcestershire sauce.
3. Form the mixture into 4 patties, each 3/4 inch (2 cm) thick.
4. Grill the hamburgers directly over medium-high heat, turning once, 3 to 5 minutes per side.
5. Check for doneness by cutting into a hamburger near the center or testing with an instant-read thermometer.
6. No pink should show on the inside, and the internal temperature should register at least 160°F (62* C) on an instant-read thermometer.

for the buns

1. In a glass measuring cup, combine one cup warm water, the milk, yeast and sugar.
2. Let stand until foamy, about five minutes. Meanwhile, beat one egg.
3. In a large bowl, whisk flours with salt.
4. Add butter and rub into flour between your fingers, making crumbs.
5. Using a dough scraper, stir in yeast mixture and beaten egg until a dough forms.
6. Scrape dough onto clean, well-floured counter and knead, scooping dough up, slapping it on counter and turning it, until smooth and elastic, 8 to 10 minutes.
7. The dough will be on the sticky side so it can be a bit messy, but keep in mind that the more flour you knead in, the tougher the buns will get.
8. Try to leave them tackier than you would a round loaf.
9. Shape dough into a ball and return it to bowl.
10. Cover bowl with plastic wrap and let rise in a warm place until doubled in bulk, one to two hours.
11. Line a baking sheet with parchment paper.
12. Using dough scraper, divide dough into 8 equal parts.
13. Gently roll each into a ball and arrange two to three inches apart on baking sheet.
14. Cover loosely with a piece of plastic wrap lightly coated in nonstick spray and let buns rise in a warm place for one to two hours.
15. Set a large shallow pan of water on oven floor.
16. Preheat oven to 400 degrees F (200 C) with rack in center. Beat remaining egg with one tablespoon water and brush some on top of buns.
17. Sprinkle with sesame seeds, if using.
18. Bake, turning sheet halfway through baking, until tops are golden brown, about 15 minutes. Transfer to a rack to cool completely.