1/2 onion, chopped
2 serrano chiles (remove seeds for a milder curry)
3 cloves garlic
1 tablespoon peanut or expeller-pressed canola oil
1 3/4 pound sirloin tip steak, cut into 3/4-inch cubes
1/2 teaspoon fine sea salt, plus more to taste
1 cinnamon stick
1 1/4 teaspoon coriander seeds
1 1/4 teaspoon ground cumin
1 teaspoon ground turmeric
1 (13.5-ounce) can light coconut milk
1 (14.5-ounce) can diced tomatoes, drained
1/2 teaspoon sugar
1 pound red potatoes, cut into 1-inch pieces
1/3 cup packed cilantro leaves