Preheat oven to 450ºF (230ºC).
Shell fava beans, discarding pods. In large pot of boiling salted water, cook beans for
5 minutes. Reserving 1 cup (250 mL) cooking liquid, drain and rinse under cold water. Let cool completely. Pinch skin of each bean to break at one end; squeeze bean out of skin. Set aside.
In large skillet, heat oil over medium-high heat. Add onion and garlic; cook, stirring, for 3 minutes or until softened. Add beans, parsley, dill, lemon rind and juice, 1/2 teaspoon
(2 mL) of the salt and half the pepper; cook for 4 minute.
Add wine, stirring to scrape up any brown bits on bottom of pan. Transfer to food processor along with 3/4 cup
(175 mL) of the reserved cooking liquid; purée. Add enough of the remaining cooking liquid to make smooth. Transfer to saucepan; keep warm over low heat.
Meanwhile, using sharp chef’s knife or carving knife, cut skate into thin fillets by cutting horizontally between cartilage and flesh. Line baking sheet with foil; brush foil well with olive oil. Place fish on prepared pan. Season with remaining salt and pepper. Roast in oven for about 7 minutes or until opaque and fish flakes easily with fork.
Arrange fish on plates; surround with purée.