2Melt the Unsalted butter in a small saucepan over low heat. In a bowl, combine the mashed Salted duck egg yolks, melted Unsalted butter, Granulated sugar (for the filling), Evaporated milk, Custard powder, and Wheat starch. Mix vigorously until a smooth, uniform paste forms.
3Cover the filling mixture and refrigerate for at least 2 hours, or until firm enough to handle and portion. Once firm, divide the filling into 10 equal portions, rolling each into a small ball.