Put 1 pound mixed baby potatoes in a medium pot; cover with cold water and season with salt. Bring to a boil; cook until tender, 15 minutes. Combine 2 tablespoons olive oil and 1 tablespoon melted butter in a large bowl. Add 1 chopped large heirloom tomato and 1 tablespoon each chopped parsley, chives and basil. Drain the potatoes; add to the bowl and toss. Season with salt and pepper.