Prep: 10 minutes
Total: 1 hour
30 ml canola oil
1 large yellow onion, sliced thinly
450 grams Yukon gold potatoes, peeled and cut into 1-inch pieces
1350 grams sweet potatoes, peeled and cut into 1-inch pieces
kosher salt, to taste
66 grams unsalted butter, softened
250 ml whole milk
50 grams raw English walnuts, plus extra toasted walnuts for garnishing
60 ml heavy cream
pinch of nutmeg
freshly ground black pepper, to taste
1. Heat the oil in a medium skillet over medium heat. Add the onions and cook, stirring, until caramelized, 20 minutes. Set aside.
2. Place all the potatoes in a large pan of salted water over a high heat. Bring to the boil and cook for 15-20 minutes, or until the potatoes are tender. Drain and let the potatoes steam-dry for about 3 minutes.
3. In a small saucepan, combine the milk, walnuts, cream, and nutmeg and bring to a simmer. Cook until the walnuts are soft, about 20 minutes. Transfer to a blender and purée until smooth.
4. Return potatoes back to the pan, adding the walnut mixture and butter, mixing and mashing well to combine. Season with salt and pepper and serve topped with the caramelized onions and toasted walnuts.