Make the dressing
Put the egg yolk, anchovies, garlic, and mustard in a food processor. With the motor running, gradually add the olive oil and process until the mixture starts to thicken and emulsify (it should have the consistency of heavy cream), about 2 minutes. With the motor still running, add the lemon juice and 1 tsp. hot water. Continue to process until the mixture reaches a soft mayonnaise consistency. Season to taste with salt and pepper and set aside.
Make the salad
Put the onion in a medium bowl, cover with cold water, and soak for 20 minutes. Drain and pat dry.
Put the potatoes in a large pot of wellsalted water. Bring to a boil over medium-high heat and cook until the potatoes aretender, 5 to 10 minutes. Drain and when cool enough to handle, cut them in half. Transfer to a large bowl and toss with the reserved onion and a couple of spoonfuls of the dressing.
Bring a large pot of well-salted water to a boil over medium-high heat. Remove the fava beans from their pods and cook them in the boiling water until tender, about 2 minutes. Drain and run under cold water to stop the cooking. Pinch the dull, olive-colored skin and slip each bean out (you should have about 2 cups beans). Discard the skins. (Alternatively, cook the haricots verts in the water until tender, 2 to 3 minutes.)
In a medium bowl, toss the tomatoes with the olives and season with a few grinds of pepper.
Arrange the potatoes and onions, tomatoes and olives, favas, and lamb on a large serving platter. Garnish with the caper berries. Drizzle with the remaining dressing and season to taste with salt and pepper.
Note: This recipe contains a raw egg. If that’s a concern, use a pasteurized egg.
nutrition information (per serving):
Photo: Scott Phillips