Heat 3 tbsp of the olive oil in a 30 cm / 12-inch skillet over medium-low heat. Add the sliced onions and a pinch of salt.

Cook the onions for 25 to 30 minutes, stirring every few minutes, until soft, deep golden brown, and jammy. Lower the heat if they start to catch. Set aside.

While the onions cook, add the rinsed lentils to a 3-quart / 2.8 L saucepan with 500 ml of the water and the bay leaf. Bring to a boil, then lower the heat and simmer for 15 to 18 minutes, until the lentils are just tender but not falling apart.

Drain the lentils through a fine-mesh sieve, reserving the cooking liquid. Discard the bay leaf. You should have close to 400 ml of liquid; top up with the remaining water if you're short.

Wipe out the saucepan and heat the remaining 2 tbsp olive oil over medium heat. Add the rinsed rice and cumin, stirring for 1 minute until the rice looks glossy.

Return the lentils to the pot along with the reserved cooking liquid, 1 tsp salt, and the black pepper. Stir once, bring to a gentle simmer, then cover and cook for 16 to 18 minutes, until the rice is tender and the liquid is absorbed.

Take the pot off the heat and let it sit, covered, for 5 minutes. Fluff gently with a fork.

Taste and add more salt if needed. Spoon onto plates and top each portion with a generous pile of caramelized onions.

Drizzle with a little of the oil left in the onion pan, add a splash of red wine vinegar if using, and serve with lemon wedges on the side.