Keema Aloo (Garam Masala-Spiced Ground Beef with Potatoes)

Ingredients

• 2 tablespoons vegetable oil
• 6 black peppercorns
• 4 green cardamom pods
• 2 black cardamom pods
• 1 cinnamon stick
• 1 red onion, halved and sliced thin crosswise
• 1 teaspoon grated garlic
• 1 teaspoon grated fresh ginger
• 1 pound 90-percent lean ground beef
• 3/4 teaspoon table salt
• 2 teaspoons ground coriander
• 2 teaspoons Kashmiri chile powder
• 1/2 teaspoon ground turmeric
• 1/2 teaspoon ground cumin
• 2 (6-ounce) vine-ripened tomatoes, cored and chopped
• 1 (8-ounce) Yukon Gold potatoes, peeled and cut into 1⁄2-inch pieces
• 1/4 cup whole-milk yogurt
• 2 tablespoons water
• 1 long green chile, halved lengthwise (optional)
• 1/4 cup chopped fresh cilantro, plus extra for garnish