How to Make It
Preheat the oven to 250°. Spread the potatoes in a large ovenproof skillet. Add 1 cup of the canola oil along with the olive oil, garlic and thyme and bring to a simmer. Cover and transfer the skillet to the oven. Bake for about 45 minutes, until the potatoes are just tender. Using a slotted spoon, transfer the potatoes to a plate. Discard the garlic and thyme. Reserve the oil for another use.
Heat a large skillet over high heat. Add the duck breasts skin side down and season with salt and pepper. Reduce the heat to low and cook until the skin is deeply golden and crisp, about 15 minutes. Spoon the fat in the skillet into a heatproof cup as it accumulates. Flip the duck breasts and cook for 3 to 4 minutes longer for medium meat. Transfer the duck breasts to a cutting board, skin side up, and let rest for 10 minutes before slicing. Wipe out the skillet.
Spoon 4 tablespoons of the reserved duck fat into the skillet and heat until shimmering. Add the potato slices and cook over high heat, turning once, until browned and crisp, about 5 minutes. Drain on paper towels and sprinkle with salt.
In a large bowl, whisk the remaining 1 tablespoon of canola oil with the vinegar and truffle oil and season with salt and pepper. Add the frisée, spinach and parsley and season with salt and pepper. Toss well. Serve the duck slices with the potatoes and salad.