Whisk 1/4 cup mayonnaise, 3 tablespoons grated parmesan, 1/2 teaspoon pepper and 1 tablespoon water. Trim 1 pound asparagus and cut into pieces; place in a steamer basket set over simmering water. Add 1 cup drained canned butter beans; cover and steam until tender, 3 to 5 minutes. Transfer to a platter. Season with salt; drizzle with the sauce and top with shaved parmesan.