Mise en place (set yourself up for control)
Pat lamb very dry (paper towels). Moisture is the enemy of browning.
Dice carrot/celery; slice onion; crush garlic.
Warm stock. Bloom saffron in 30 ml / 1 fl oz hot stock (or hot water) and set aside.
Preheat oven to 160°C / 320°F.
Season and sear the lamb
Heat a heavy Dutch oven over medium-high for 2 minutes. Add olive oil.
Season lamb with salt and pepper just before it hits the pan. Sear in batches—leave space between pieces. Brown deeply on 2–3 sides, about 8–12 minutes total per batch. Transfer to a tray.
Aromatic base (sofrito, but cleaner)
Lower heat to medium. If the pot is dry, add a touch more oil (5 g / 0.2 oz).
Add onion with a pinch of salt; sweat 5 minutes until glossy. Add carrot and celery; cook 6–8 minutes until softened and sweet. Add garlic, rosemary, and myrtle berries (or bay). Cook 60 seconds until fragrant. Stir in tomato paste and cook 2 minutes to caramelize lightly.