Cream the butter, shortening, and icing sugar together in a bowl until light and fluffy, about 8 minutes. Add the egg and pineapple essence, if using, and mix well. Fold in the all-purpose flour, corn flour, and milk powder gently. Refrigerate for 20 minutes. Divide the dough into 30 equal pieces and wrap each with the pineapple filling. Press it into a square mold and bake at 170°C (338°F) for 15-20 minutes. Turn it around and bake for another 15 minutes until golden brown. Place the pineapple in a food processor and pulse until pureed, stopping to scrape the sides occasionally for about 18 to 20 pulses. Pour into a Dutch oven. Place the winter melon in the food processor and pulse until very finely shredded, about 20 to 22 pulses. Transfer to the Dutch oven. Cook the combined mixture over medium-high heat, stirring occasionally, until most of the liquid has evaporated and the winter melon begins to turn translucent, about 20 minutes. Reduce the heat to medium, add the granulated sugar, and cook until the mixture thickens, about 8 minutes. Stir in the maltose syrup and cook, stirring constantly, until the mixture is very thick, sticky, and uniformly light amber in color, about 10 to 12 minutes. Transfer the mixture to a shallow bowl and refrigerate until cool. Divide into 1 teaspoon portions.
