The olive oil emulsifies with the braising liquid to create a silky sauce that deliciously coats the bright spring veggies. Thin lemon slices, charred and caramelized in a cast-iron pan, make a nice garnish.
Cook fava beans 1 minute in boiling water. Drain and plunge immediately into ice water. Drain well. Remove membranes from beans; discard membranes. Set beans aside.
Heat a large high-sided sauté pan over medium heat. Add oil to pan. Add yellow onions; cook 6 minutes or until tender, stirring occasionally. Add fennel bulb and potato; cook 5 minutes, stirring occasionally. Stir in artichokes, green onions, fennel seeds, and carrots.
Add wine; cook 1 minute. Add 1 1/2 cups water, preserved lemon, salt, and pepper. Reduce heat to low, and simmer for 10 minutes or until vegetables are tender.
Combine 3 tablespoons lemon juice and cornstarch in a small bowl; stir until smooth. Add cornstarch mixture to pan; increase heat to high, and cook 2 minutes or until sauce thickens. Stir in remaining 3 tablespoons juice and fava beans. Sprinkle with dill and reserved fennel fronds.