Garlic and Chile Roasted Dungeness Crabs

Name: Garlic and Chile Roasted Dungeness Crabs
Ingredients: 1 1/2 teaspoons salt, plus more for cooking the crabs; 1 lemon, thinly sliced; 1 head garlic, minced, peels reserved; 1 onion, minced, peel reserved; 4 large Dungeness crabs*, 1 1/4 to 1 1/2 pounds each; 1 cup (2 sticks) unsalted butter; 1 cup olive oil; 2 teaspoons crushed red pepper, or 6 to 8 fresh red chiles, such as serrano, minced and seeded, or to taste; 1/2 teaspoon ground black pepper; 3/4 cup chopped fresh parsley or cilantro leaves