01 - Heat olive oil in a large pot over medium heat. Add the chopped onion, diced carrots, and diced celery. Sauté for 5 to 7 minutes, stirring occasionally, until the vegetables are softened and the onion is translucent.
02 - Stir in the minced garlic, tomato paste, smoked paprika, and dried thyme. Cook for 1 minute, stirring constantly, until fragrant and the tomato paste darkens slightly.
03 - Add the rinsed lentils, bay leaf, and vegetable broth to the pot. Bring to a boil, then reduce the heat to low and simmer uncovered for 20 minutes, or until the lentils are tender. Season with salt and pepper to taste.
04 - While the stew simmers, combine the flour, baking powder, and salt in a mixing bowl. Cut in the cold cubed butter using a fork or pastry cutter until the mixture resembles coarse crumbs. Stir in the chopped parsley if using, then pour in the milk. Stir gently just until the dough comes together; avoid overmixing to keep the dumplings light and tender.
05 - Drop tablespoon-sized portions of the dumpling dough evenly onto the surface of the simmering stew. Cover the pot tightly with a lid and cook for an additional 15 minutes without lifting the lid, until the dumplings are puffed and cooked through.
06 - Remove and discard the bay leaf. Taste the stew and adjust the seasoning with additional salt and pepper if needed. Ladle into bowls and serve hot.