Shepherd's Pie with Kheema + Chouriço

Preheat the oven to 400°F [204°C]. 

To prepare the lamb kheema, heat the oil in a large skillet over medium-high heat. Add the onion and sauté until it turns translucent, 4 to 5 minutes. Add the garlic, ginger, and green chilli and sauté for 1 minute. Add the tomato paste, garam masala, turmeric, and red chilli powder and cook until the spices are fragrant, 30 to 45 seconds. Add the peas and carrots, and sauté until tender, 8 to 10 minutes. Remove the chouriço from the casing and break it into small bits. Add it to the skillet and cook until the sausage starts to brown, 4 to 5 minutes. Break the lamb into chunks and add it to the skillet. Sauté until the lamb starts to brown, 4 to 5 minutes. At this stage, you can remove some of the excess fat using a large spoon and discard. Sift the flour over the meat and fold it in to coat evenly. Add the vinegar and cook, stirring, over low heat until the liquid has almost completely evaporated. Remove from the heat and stir in the cilantro and fish sauce. Transfer the meat to a large baking dish and level with an offset spatula. 

Rinse and scrub the potatoes under running tap water. Place the potatoes in a large pot with enough salted water to cover them by 1 in [2.5 cm]. Bring to a boil over medium-high heat, then lower the heat to medium-low. Cook until the potatoes are completely tender but not mushy, 20 to 30 minutes. Drain the potatoes and set them aside until cool enough to handle.

Peel the potatoes and discard the skins. Mash the potatoes in a large bowl with the crème fraîche, butter, and pepper until smooth. Taste and season with salt. Spoon the mixture onto the meat in the baking dish. Level with an offset spatula. Sprinkle the panko over the layer of mashed potatoes and bake until the top is golden brown, 20 to 25 minutes. Remove from the oven and let rest for 10 minutes before serving.