– 2 teaspoons sea salt, divided – 2 cups diced baby potatoe – 1 cup diced peeled carrot – 1 cup fresh English peas (or frozen petite peas) – 4 tablespoons unsalted butter, divided – 1 cup diced fresh fennel bulb – 1 large leek, stem and dark green leaves trimmed, thinly sliced – 1 cup trimmed tiny mushrooms (beech, enoki, or button) – 2 large cloves garlic, minced – 1 cup tender stalks of asparagus, cut into ½-inch length – 2 tablespoons all-purpose flour, plus additional for rolling puff pastry – 1 ½ cups vegetable stock – 1 cup sour cream – 1 tablespoon whole-grain mustard – ½ teaspoon freshly ground black pepper – 1 tablespoon fresh thyme leave – 1 tablespoon finely chopped fresh Italian parsley – 1 tablespoon finely chopped fresh tarragon leave – 1 tablespoon finely chopped fresh chive – 1 sheet frozen puff pastry, thawed overnight in the refrigerator – 1 egg, lightly beaten