Taiwanese Pineapple Cakes

Name: Taiwanese Pineapple Cakes
Ingredients: Two 8-ounce cans crushed pineapple, drained well; 1/2 cup granulated sugar; 3 tablespoons dark corn syrup; 1 tablespoon cornstarch; 1 teaspoon fresh lemon juice; 1 cup cake flour, plus more for dusting; 6 tablespoons cold unsalted butter, cut into small cubes; 1/4 cup confectioners' sugar; 2 tablespoons nonfat milk powder, such as Carnation; 2 tablespoons original custard powder, such as Bird's (see Cook's Note); Pinch kosher salt; 1 large egg yolk; Nonstick cooking spray, for the molds