Very satisfying version of this Indian dish, and pretty easy to make as well.
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, peeled 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
Place mustard seed, cumin seed, and coriander seed in a skillet and toast over high heat until spices begin to smell toasted, about 3 minutes. Transfer to a mortar and pestle or spice grinder and process until fine.
Heat vegetable oil in a large pot over medium heat until oil is shimmering. Season chicken thighs with salt and add to pot skin side down, cook until skin is golden, about 5 minutes then flip and cook until other side is also brown, about another 4 minutes. Transfer to a plate and reserve.
Add onion, carrot, and celery to the pot and cook, stirring often until onions are translucent, about 5 minutes. Add curry powder and toasted spiced and stir until the vegetables are evenly covered with the spices. Add garlic, ginger, sweet potato, apple and plum tomato and stir to coat. Add lentils then return chicken thighs to the pot. Cover with broth or water and bring to a simmer. Cook until potatoes and lentils are soft and soup has thickened, about 1 hour.
Remove thighs from the soup and shred the meat and skin then return to the pot. Season to taste with salt and pepper and serve garnished with yogurt, cilantro, and red pepper flakes.