01 - Heat olive oil in a large pot over medium heat. Add the diced onion, sliced carrots, sliced celery, and minced garlic. Sauté 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 mixing 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 lentil stew is at a lively simmer. Drop spoonfuls of dumpling dough (about 1 tbsp each) onto the surface of the 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 seasoning with salt and pepper as needed. Sprinkle with chopped fresh parsley before serving, if desired.