INGREDIENTS
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1/4 cup extra-virgin olive oil
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1 yellow onion, thinly sliced
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1 fennel bulb, cored and thinly sliced, 2 tablespoons fronds chopped and reserved
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2 pounds sweet Italian sausage, casings discarded
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2 tablespoons fennel seeds
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2 tablespoons chopped rosemary
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6 garlic cloves, thinly sliced
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1 tablespoon pepper, plus more for seasoning
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Kosher salt
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2 eggs, beaten
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4 medium red onions, peeled and halved
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One 5-pound, boneless pork shoulder, butterflied 1 inch thick (roughly a 10-by-14-inch rectangle)—have your butcher do this