Core the cabbage and blanch it in boiling water for 10–15 minutes, removing the leaves as they soften. Set leaves aside to cool, then trim the thick stems to ease rolling.
In a large bowl, combine the soaked rice, minced lamb, salt, black pepper, white pepper, cinnamon, 7-spice, cumin, coriander and vegetable oil. Mix well to combine.
Place a leaf on a flat surface, add a spoonful of filling near the base, and roll tightly into a small log, tucking in the sides if necessary. Repeat with remaining leaves and filling.
Line the bottom of a large pot with torn or leftover cabbage leaves. Arrange the stuffed cabbage rolls tightly in layers, sprinkling peeled garlic cloves and dried mint between each layer.
Add enough water to barely cover the rolls. Place a heatproof plate over the rolls to keep them submerged. Bring to a boil, then reduce heat to low, cover, and simmer for 1 to 1½ hours, or until cabbage and rice are tender.
Once cooked, pour lemon juice over the rolls and let them rest for 10 minutes before serving. Adjust lemon to taste.