Trim the tops and bottoms of the corn husks; the hairy parts tend to catch fire and soak them with husk on for 20 minutes in water before grilling.
Preheat the BBQ on high heat (500°F). Arrange the corn husks over the grill. Reduce to medium/high (400°F), cover and cook 18-20 minutes, turning every 5 minutes until husks are blackened on all sides.
While the corn is grilling, melt 1 stick butter in a small saucepan. Press 4 cloves garlic over the butter and heat just to a simmer. Add 1/2 tbsp Sugar, 1 tsp salt, 1 tsp pepper, 1/2 tsp cumin and lime juice. Stir to combine. Heat another minute and remove from heat.
Remove Corn from the grill, carefully peel husk off but don't rip it off, instead use it as a handle.
Generously brush corn with butter mixture and serve immediately.