Wash the vegetables in a large bowl of cold water and blot dry. Trim the fennel of any stringy layers, and slice thinly crosswise. Peel the outer leaves of the artichokes to reveal the pale green hearts, and slice into thin wedges. Peel the carrots and slice lengthwise. Cut the cauliflower into thin slices, or break it up into small florets. Separate the leaves of the Belgian endive and radicchio or Treviso. Snap off and discard the tough bottom ends of the asparagus and slice the spears into quarters lengthwise. Cut the turnips and radishes into quarters, leaving the tops attached, or leave whole if they are small. Clean the spring onions and slice in half lengthwise. Sprinkle everything lightly with sea salt and arrange the vegetables on a platter, tossing them together to create a colorful display. Scatter the fava beans over the top.

Rinse and fillet the anchovies. In a mortar, pound the garlic to a paste with a little salt and pepper. Add the anchovies and pound until roughly mashed. Warm the olive oil and butter over medium-low heat. Add half the anchovy mixture, the red wine vinegar, and lemon zest, and gently simmer for 2 minutes. Stir in the remaining anchovy mixture, taste for salt and pepper, and transfer the sauce to a warmed bowl or individual ramekins.