1. In a large, heavy skillet, heat the oil and butter over medium-high heat. When the butter melts and foam subsides, sauté the onion for 3-4 minutes, until soft and starting to turn golden.
2. Add the garlic and potatoes and cook for another 3-4 minutes until the potatoes are starting to turn golden on the edges.
3. Add the ginger and curry paste and cook for another minute.
4. Add the lentils, cilantro (optional), vegetable stock, and coconut milk. Stir to combine well and reduce the heat to a simmer.
5. Cover and cook, stirring occasionally, for 30 minutes, or until the potatoes are tender. Add a little water, stock, or coconut milk if it gets too thick.
6. Add the lime juice and season with salt (optional). Serve hot.
Curry powder used for recipe costing and nutrition analysis.