Method
Preheat oven to 425 degrees.
Combine the chicken, potatoes, garlic, 1 Tablespoon of curry mustard (or regular mustard), 2 tablespoons of the olive oil, 1 teaspoon of the salt and 1/2 teaspoon of the black pepper in a large bowl and toss to coat. Arrange the chicken and potatoes on a sheet pan in a single layer.
Combine the onions, mushrooms, carrots and remaining 2 tablespoons olive oil, 1 teaspoon salt, and 1/2 teaspoon black pepper in a large bowl and toss to coat. Spread the onions and mushrooms between and around the chicken pieces (these can be piled up—no need to arrange them in an even layer). Roast for 30 minutes, rotating the pan halfway through the cooking time.
Meanwhile, in a small bowl, stir together the remaining 2 tablespoons of curry mustard with the coconut milk.
After 30 minutes of roasting, remove the pan from the oven and toss the onions and mushrooms to release any pieces that are sticking to the pan. Smother each chicken piece with the cream mixture, and drizzle the excess cream mixture across the whole sheet pan to use it up. Roast for another 20 minutes, until the chicken is golden-brown and its internal temperature reaches 160F with a thermometer inserted into the thickest part of a piece.
Sprinkle the optional fresh cilantro over the top and serve.
