Preheat the oven to 400˚F.

Combine the lentils, 1/2 teaspoon of salt, and 4 cups of water in a large pot over high heat. Reduce heat to a simmer, and cook about 20 minutes, until tender but not mushy. Drain and set aside.

In an oven-safe pot, combine the rice, 1/2 teaspoon of salt, and 1 1/2 cups of water over medium heat. Bring to a boil, then cover and transfer to the oven. Cook for 17 minutes, until perfectly cooked. Remove from oven and fluff with a fork. Set aside.

In a large sauté pan, heat the butter and 2 tablespoons of the oil over medium-low heat. When the butter has melted, add the sliced onions and toss to coat in butter and oil. Sauté for 5 minutes, until the onions have softened and released some of their liquid. Raise the heat to medium, and cook until onions are very soft and golden brown, about 10-12 minutes. Add the last tablespoon of oil and raise heat to high. Cook for 3-4 minutes, until the bottom layer of onions is nicely crisped. Don't stir often or the onions won't crisp.

Combine the lentils and the jasmine rice in a large bowl. Fold in most of the onions. Allow to rest for at least 15 minutes. Taste and add more onions if desired. 

In a small bowl, mix together the yogurt, cinnamon, cumin, corainder, paprika, fresh mint, lemon juice, lemon zest, and remaining 1/4 teaspoon of salt. Serve the yogurt sauce alongside the mujaddara.