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 to 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 returns to a lively simmer. Drop spoonfuls of dumpling dough, about 1 tablespoon each, onto the surface of the stew to make 8 to 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 with salt and pepper as needed. Sprinkle with chopped fresh parsley before serving, if desired.