This simple side dish lends a gorgeous splash of color and a delicious, buttery texture to just about any protein-centered dinner. To prepare it, we simply cook the peas in water, mix with a not-small amount of butter, then mash and perk them up with lemon juice. Flat-leaf parsley and fresh tarragon add elegance and depth of flavor, while chives provide a sharp bite and a gorgeous, dark-green contrast to the bright, verdant peas. It all adds up to something much tastier than you might imagine and delicate enough to pair with a lightly seasoned filet of fish cooked sous vide, or even something as rich as fish and chips.