Hong Kong style mango pancake (芒果班戟)

Name: Hong Kong style mango pancake (芒果班戟)
Prep time: 15 min
Cook time: 15 min
Total time: 30 min
Cuisine: Chinese
Ingredients: 240 ml milk (1 cup); 50 g all-purpose flour (⅓ cup, see note 1); 30 g cornstarch (or custard powder, ¼ cup, see note 2); 25 g powdered sugar (¼ cup ); 3 medium eggs (lightly beaten); 2 teaspoon butter (melted ); 300 ml double cream (or whipping cream, 1¼ cups ); ½ teaspoon vanilla extract; ½ tablespoon powdered sugar; 2 large mangoes (peeled and cut into chunks)