Preheat the oven to fan forced 180°C/200°C/400°F/Gas mark 6.
Place pistachios on a roasting tray and bake in the oven for 3-4 minutes until golden.
Remove nuts from oven and set aside. On the same tray, place Brussels sprouts with half the olive oil and salt and pepper, toss to coat well - roast for 20 minutes, until the sprouts are starting to open out and are brown and crispy on the edges.
While the sprouts are roasting, make your dressing: mix lemon juice, mustard and remaining olive oil together with salt and pepper. Taste and add more lemon or mustard if desired.
Allow to cool or serve hot with pistachios, cranberries and dressing drizzled over the top.
Notes
Store leftovers in an airtight container in the refrigerator for up to 3 days. Serve cold.