Mulligatawny Soup

Ingredients

• 1/2 teaspoon whole mustard seeds
• 1/2 teaspoon whole cumin seed
• 1/2 teaspoon whole coriander seed
• 2 tablespoons vegetable oil
• kosher salt and freshly ground black pepper
• 1 pound (about 3 large) chicken thighs
• 1 onion, finely chopped (about 1 cup)
• 1 medium carrot, finely chopped (about 3/4 cup)
• 1 celery rib, finely chopped (about 1/2 cup)
• 1 tablespoon curry powder
• 3 medium garlic cloves, finely chopped (about 1 tablespoon)
• 1 inch piece fresh ginger, finely grated
• 1 sweet potato, peeled and cut into 1/4 inch pieces
• 1 apple peel and cut into 1/4 inch pieces
• 1 plum tomato, cut into 1/4 inch pieces
• 1/2 cup dry red lentils
• 6 cups homemade or store-bought low sodium chicken broth, or water
• greek yogurt, to garnish
• finely chopped cilantro, to garnish
• red chili flakes, to garnish