Chop sweet potatoes into quarters and place in a large pot. Cover with water and bring to a full boil. Cook the potatoes 20 to 25 minutes at a controlled boil, until very soft when poked with a fork. Drain the water, transfer potatoes to a cutting board, and chop when cool enough to handle. Transfer potatoes to a large serving bowl or mixing bowl.

While potatoes are cooking, whisk together the pesto sauce, ricotta cheese, cider vinegar, olive oil, mustard, and salt.

Pour the ricotta-pesto dressing over the sweet potatoes and stir (or mash) until everything is coated. Taste the potato salad for flavor, and add more pesto sauce and/or salt to taste. Either serve hot, or place in the refrigerator until chilled and serve cold.