Note: Purple cauliflower and potatoes are available at farmers markets and select Bristol Farms and Whole Foods. White cauliflower and potatoes can be used.
1 tablespoon butter
1 leek, white part only, thinly sliced (1/2 cup)
3 medium purple potatoes, peeled and quartered (about 1 1/2 cups)
Florets from 2 small heads purple cauliflower (3 1/2 cups)
4 cups whole milk
1/2 teaspoon kosher salt
1/8 teaspoon white pepper
Walnut oil for garnish
1. In a medium saucepan, melt butter over medium-low heat, add leeks and cook until soft, about 5 minutes. Add cauliflower, potatoes, milk, white pepper and salt and bring to a simmer. Cover and simmer on low heat until vegetables are soft, about 25 minutes. Do not boil.
2. Remove the vegetables from the heat, let cool slightly and puree them in a blender, with an immersion blender or in a food mill. (If using an immersion blender, cover with a towel to avoid splattering.)
3. If serving warm, reheat gently and serve with a drizzle of walnut oil. If serving cold, chill in the refrigerator before serving (also with walnut oil).