Drain pineapple and reserve juice for another recipe.
Add sugar and pineapple to a small skillet and cook over medium heat until mixture is thick and caramelized, about 30 minutes. Let cool completely.
pastry
Preheat oven to 350°F.
Cream together butter and sugar. Add the beaten egg and mix until incorporated.
Sift in flour, milk powder and salt to the butter mixture to form a soft dough. If the dough is too dry, add a bit more of the leftover egg.
cakes
Separate the dough into 24 balls. Roll each ball into an oblong shape that will fit in the cup of a mini muffin pan, about 2 inches by 4 inches.
Place the dough into the cup and leave one end hanging over. Add about a teaspoon of pineapple jam. Fold over the remaining dough on top of the jam and press gently.
Repeat with remaining balls. Bake until pastry starts to brown, about 20 minutes. Move cakes to rack to cool.