Prepare the pastry: Cream together the softened unsalted butter and powdered sugar. Add in the egg yolks and vanilla, and mix until well combined.
Combine dry ingredients: In a separate bowl, whisk together the cake flour, cornstarch, milk powder, and salt.
Form the dough: Gradually add the dry ingredients to the wet mixture, mixing until a dough forms. If the dough is too sticky, add a bit more cake flour.
Prep the filling: Ensure the pineapple jam is chilled and ready to use.
Assemble the tarts: Portion the dough and flatten each piece to form a small disc. Place a small amount of pineapple jam in the center, then wrap and seal the dough around the jam.
Apply egg wash: Mix the egg yolk, oil, and a tiny pinch of salt for the egg wash. Brush the surface of each tart gently.
Bake: Bake in a preheated oven until golden brown. Please watch the video for detailed instructions on temperature and timing.