Bring 2 cups of water to a rolling boil. Turn the heat off. Add the peas and cook for exactly 2 minutes. Quickly drain the water off the peas and add them to the ice bath.
In a large bowl, add the cooked potatoes, green onions, mayonnaise, salt, pepper, and the buttermilk. Gently toss the potatoes to coat. Toss in the peas gently.
Turn the Green Spring Pea Potato Salad into a bowl/platter.
Garnish with lemon slices, a sprig of thyme, and pickled purple onions