Put the fava beans in a small saucepan and cover with about 4 cups of cold water. Add the shallot, garlic, and 1 teaspoon salt. Bring to a boil, turn down the heat, and simmer for about 40 minutes or until the beans are falling apart. Cool to room temperature. Drain, reserving ½ cup cooking liquid. Transfer the beans and garlic to a food processor. Add the lemon juice, cumin, cayenne, and pepper to taste, and puree until very smooth. With the machine running, add the olive oil in a slow, steady drizzle. Don't worry if the texture is soupy; the puree will stiffen as it chills. Once chilled, stir in the chopped mint and adjust the seasoning.