Sprinkle ½ teaspoon of ground saffron over a few ice cubes in a small bowl and let them melt at room temperature.
In a large bowl, mix 680g of ground lamb, 680g of ground beef (80% lean), and 340g of grated white onion, weighed after squeezing out its juice, by hand for about 15 minutes.
Add 1 tablespoon of kosher salt, 1 teaspoon of black pepper, and the saffron water. Knead for at least 10 minutes more, until it turns paste-like, then cover and refrigerate for 1 hour. Meanwhile, light a charcoal grill.
Press the meat around flat skewers 1in / 2.5cm wide in an even layer about 6in / 15cm long.
Cook 6 Roma tomatoes over the hot coals for 10-15 minutes. Cook the kebabs alongside for 3-4 minutes, turning them constantly, until they reach 160°F / 71°C.
