Yield 8 servings
¼ cup walnuts, roughly chopped
4 ounces fennel fronds, thickest stems removed, rinsed and drained well
2 ounces spinach, stemmed, washed thoroughly to remove all grit and drained well
½ cup grated Parmigiano-Reggiano cheese
¼ cup extra-virgin olive oil
1 small garlic clove, roughly chopped
1 teaspoon lemon juice
½ cup plain Greek yogurt
Kosher salt and freshly ground black pepper, to taste
2 pounds new potatoes or fingerlings
2 tablespoons kalamata olives, drained well and roughly chopped
Preheat oven to 350°. Spread walnuts in a single layer on a baking sheet and toast until aromatic and golden, about 5 minutes. Let cool.
Combine nuts, fennel fronds, spinach, cheese, olive oil, garlic and lemon juice in food processor and purée. (You might need to do this in a couple batches, depending on the size of the food processor bowl.) Add a touch more olive oil if needed to achieve a smooth consistency.
Stir in yogurt and season to taste with kosher salt and black pepper.
Thin out with a bit of water if needed to achieve a good pouring consistency.
Boil potatoes in a pot of well-salted water until a knife inserted into the fattest potato meets no resistance. Pour into a colander and drain well. Place potatoes in serving dish and pour the fennel yogurt sauce over them. Garnish with kalamata olives.