Melt 50gm butter in a casserole over low heat, add onion and garlic and stir occasionally until tender and light golden (25-30 minutes). Add beans, fennel, verjuice, sugar and 125ml water. Season to taste, cover with a lid and braise, stirring occasionally, until very tender (2½ hours). Add parsley, cook for 10 minutes, then set aside to cool.
Meanwhile, blanch tomatoes (20-30 seconds), refresh, peel, quarter, remove seeds and set aside.
Preheat oven to 160C. Divide bean mixture among four 14cm-diameter, 6cm-deep baking dishes. Top each with a snapper fillet, then tomato, capers and anchovies, and season to taste.
Pull apart kataifi and place in a bowl. Melt remaining butter and toss with kataifi and sesame seeds. Place a quarter of kataifi over each dish, pat down lightly to cover and bake until golden and cooked through (40 minutes). Serve hot.
Note Kataifi is available from Greek