Mushroom Spring Rolls with Creamy Ginger Sauce

Name: Mushroom Spring Rolls with Creamy Ginger Sauce
Ingredients: 3 tablespoons unsalted butter; 1/2 pound oyster mushrooms, cut into 1/2-inch pieces; 1/2 pound shiitake mushrooms, stems discarded, caps sliced 1/4 inch thick; 1/2 pound cremini mushrooms, sliced 1/4 inch thick; 2 tablespoons Shaoxing wine or dry sherry; 2 tablespoons soy sauce; Salt and freshly ground pepper; 2 tablespoons extra-virgin olive oil; 2 garlic cloves, thinly sliced; 1 plump lemongrass stalk, tender white inner bulb only, minced; 1 red Thai chile, minced; 1 medium shallot, minced; 1 tablespoon plus 1 1/2 teaspoons minced fresh ginger; 1/2 teaspoon finely grated lemon zest; 10 thin egg roll or spring roll wrappers; 1 large egg, beaten; 1/4 cup mayonnaise; 1/4 cup vegetable oil, plus more for frying; 1 tablespoon chopped tarragon; 1 tablespoon fresh lime juice; 1 tablespoon rice vinegar; 10 Boston lettuce leaves, halved