01 - Heat olive oil in a large pot over medium heat. Add the diced onion, sliced carrots, sliced celery, and minced garlic. Cook until the vegetables are softened, about 5 minutes.
02 - Stir in the rinsed lentils, diced tomatoes with their juice, vegetable broth, bay leaf, dried thyme, smoked paprika, salt, and pepper. Bring to a boil, then reduce the heat, cover, and simmer for 25–30 minutes until the lentils are tender. Remove and discard the bay leaf.
03 - While the stew simmers, whisk together the flour, baking powder, and salt in a bowl. Add the cold diced butter and rub it in with your fingertips until the mixture resembles coarse crumbs. Stir in the milk until just combined; be careful not to overmix.
04 - Increase the heat so the stew reaches a lively simmer. Drop spoonfuls of dumpling dough (about 1 tablespoon each) onto the surface of the simmering stew, yielding 8–10 dumplings. Cover the pot tightly and cook for 15 minutes without lifting the lid, until the dumplings are puffed and cooked through.
05 - Taste the stew and adjust the seasoning as needed. Sprinkle with fresh parsley before serving, if desired.