Keema Cottage Pie

Name: Keema Cottage Pie
Ingredients: 2 pounds medium or large Yukon Gold potatoes; 1 tablespoon plus 2 teaspoons kosher salt, divided, plus more as needed; 1 tablespoon garam masala; 2 teaspoons Kashmiri chili powder; 2 1/2 teaspoons ground turmeric, divided; 2 medium white or yellow onions; 5 cloves garlic; 1 (2-inch) piece ginger; 1 to 2 serrano chiles; 3 tablespoons canola oil; 1/4 tomato paste; 2 pounds lean ground beef; 1 1/2 cups water; 3/4 cup whole milk; 1/2 teaspoon freshly ground black pepper, divided; 4 tablespoons unsalted butter, divided; 1 1/2 cups frozen peas; 1/3 medium bunch fresh cilantro; Plain, full-fat yogurt, for serving