Start by preparing the filling: Roll the pineapple jam into small balls, approximately 6 grams each, to make wrapping easier later. Keep them refrigerated while you prepare the dough to maintain their firmness.

For the egg wash, whisk together egg yolks, oil, and vanilla extract in a small bowl until the mixture is smooth and free of lumps. Set aside.

Prepare the dough: In a separate bowl, whisk together all dry ingredients — cake flour, cornstarch, milk powder, salt, and cheese (if using). Allow the butter and egg yolk to rest at room temperature for around 30 minutes, or until the butter is soft but not melted. Cutting the butter into small cubes helps it soften more evenly, especially in cooler climates.

In a mixing bowl, combine the softened butter and icing sugar. Use a rubber spatula to gently mix until just combined — avoid overmixing, as excessive aeration can make the finished tarts fragile. Add the egg yolk and continue to stir until the mixture becomes creamy and smooth. Gradually fold in the dry ingredients, working with a sturdy spatula. The dough may appear crumbly at first but will eventually come together into a soft, slightly sticky consistency. Cover and refrigerate for about 15 minutes to firm it up; this brief chill makes the dough easier to handle without becoming too stiff.

Shape the tarts: Preheat your oven to 320°F (160°C) if using a conventional oven, or 300°F (150°C) for a convection oven. Remove the dough from the refrigerator and portion it into 10-gram pieces, using a kitchen scale for accuracy. Roll each piece into a smooth ball for uniform baking. Flatten each ball into a small circle, about 2½ inches wide, and place a chilled pineapple jam ball in the center. Gather the edges of the dough to enclose the filling completely, pinching the seams to seal. Arrange the filled tarts seam-side down on a parchment-lined baking sheet.

If your kitchen is warm, chill the shaped tarts in the freezer for about 30 minutes before baking to help them maintain their shape. Otherwise, you may proceed directly to baking.

Bake the tarts on the middle oven rack for 20 minutes. They will remain pale and slightly soft at this stage — this is normal. Remove the tray from the oven and brush the tarts evenly with the prepared egg wash. Repeat the brushing process a second time for an extra glossy finish and deeper golden hue. Return the tray to the oven and bake for an additional 15 minutes, or until the tarts turn beautifully golden brown.

Cool the tarts in the pan for about 5 minutes before transferring them carefully to a wire rack. Allow them to cool completely before storing.

Storing: These tarts actually taste better the next day once their flavors have settled. On the day of baking, they may seem a little dry, but after resting for 24 hours, their texture becomes perfectly tender and buttery. Store them in an airtight container at room temperature for up to 2–3 weeks. For longer storage, you can freeze them in a freezer-safe container for up to one month. Thaw at room temperature before serving — they’ll taste as fresh as the day they were baked.