Heat the oven to 375°F and lightly butter a 9-by-13-inch baking dish.

Peel and core the apples while keeping them as whole as possible. Make a small cavity in the center of each apple for the sugar-spice filling.

Whisk together flour, baking powder, and salt. Cut in the shortening or cold butter until coarse crumbs form, then stir in the milk just until a soft dough comes together.

Turn the dough onto a lightly floured surface and divide it into six portions. Roll each portion into a roughly 7-inch square about 1/8 inch thick.

Place one apple in the center of each square and fill the cavity with the sugar, cinnamon, and optional nutmeg. Bring the corners over the apple and pinch the seams firmly closed.

Arrange the dumplings seam-side up in the prepared baking dish. Make sure the dough is fully sealed around each apple.

Combine the syrup sugar, water, butter, salt, and optional cinnamon in a saucepan. Bring the mixture to a boil, stirring until the sugar dissolves, then remove it from the heat and stir in the vanilla.

Pour the hot syrup around and over the dumplings. This liquid will bubble around the pastry and help create the rich sauce.

Bake for 40–50 minutes, until the pastry is golden brown and the apples are tender when pierced with a skewer or thin knife. Spoon syrup over the dumplings before serving.