Skillet Poached Cod with Spinach and Butter Beans

Name: Skillet Poached Cod with Spinach and Butter Beans
Ingredients: 4 (6-ounce) skinless cod fillets , 1 to 1½ inches thick; ¾ teaspoon table salt , divided; 4 tablespoons unsalted butter; 1 leek , white and light-green parts only, halved lengthwise, sliced thin, and washed thoroughly; 3 garlic cloves , sliced thin; ¼ teaspoon red pepper flakes; 1 (15-ounce) can butter beans , undrained; 5 cups (5 ounces) baby spinach; 1 tablespoon lemon juice; 2 tablespoons chopped fresh dill , divided