Prep: Remove the puff pastry from the freezer and thaw according to package directions. Preheat the oven to 400 F and set a lined baking sheet aside.: As the oven warms, you should feel a gentle excitement and smell a faint neutral pastry scent in the air, not yet buttery or toasty. The thawing stage is critical because if the puff pastry is too warm it will lose its structure and become sticky, making clean cuts and folds difficult. A good indicator that pastry is ready is when it is pliable but still cold to the touch, with faint seams visible between layers. Avoid forcing the sheets open if they resist, because that tears delicate layers. Common troubleshooting is having pastry get too soft on a hot counter; if that happens, pop it back in the fridge for 10 to 15 minutes to firm up before rolling.
Cook the Apples: Melt the butter over medium heat in a medium pan. Add the apples to the pan along with the brown sugar, water, cinnamon, ginger, cardamom, nutmeg, and salt. Mix well until the apples are evenly coated in spice. Sauté for 7 to 10 minutes, stirring occasionally, until the apples are tender and there is liquid on the bottom of the pan.: When the butter has melted and the pan gives off a faint nutty aroma, add the diced apples , brown sugar , and spices. The mixture should sizzle softly as the juices release, and within moments you will hear gentle bubbling and see glossy syrup forming on the bottom of the pan. Stir occasionally so the apples cook evenly and each piece is coated, aiming for tender but still slightly holding shape, about 7 to 10 minutes. The smell will turn warmly spiced and sweet, signaling caramelization. If the pan cooks too hot, the sugars can scorch and taste bitter, so lower the heat if you notice dark spots forming.
Thicken the Filling: dissolve the cornstarch in water, add to the apples, and stir rapidly. Remove the apples from the heat and set aside while you prepare the puff pastry.: The cornstarch slurry should be clear and smooth before adding, and once stirred into the hot fruit it will transform the liquid into a glossy, thickened sauce within moments. You will see the juices go from runny to slightly syrupy and cling to the apples , which is the visual cue that the filling is set. This texture matters because it prevents the turnovers from becoming soggy while baking. If you add undissolved cornstarch, it can form gritty lumps, so make sure it is fully dissolved first.
Cut the Puff: Lightly dust a cutting board or large surface with half of the flour, then place one sheet of puff pastry on top. Use a rolling pin to roll the pastry out into an 11" by 11" square, then cut into four equal squares.: Lightly dusting the board keeps the dough from sticking and helps you create a clean square when rolling to 11 by 11 inches. You should feel a gentle resistance as the rolling pin passes and hear a soft, dry pastry whisper rather than a sticky pull. Neat edges make folding easier and promote even baking. If the dough begins to stick or get warm, pause and chill it, because overworking warm pastry reduces flakiness.
Fill the Pastry: Fill one half of each pastry square with the cooked apple mixture, leaving a 1/2" border on the edges. Brush the edges of the pastry with milk, then fold the other half of the pastry over to form a triangle; use a fork to pinch the edges together, then transfer to the baking sheet. Repeat steps 4 and 5 until you have 8 turnovers.: The filling should be cool or just warm when you spoon it onto the pastry, so the layers of dough do not steam and go soggy. Leave a 1/2 inch border so the edges can be sealed properly; when you brush the border with plant based milk , you create a glue that helps the pastry hold its shape as it bakes. Pinch edges firmly with a fork to create a sealed seam, which prevents leakage and encourages a pretty crimp pattern. A common error is overfilling, which leads to bursting during baking, so keep the portion modest and consistent.
Bake: Cut 1-2 small slits in the top of each pastry with a knife to allow for ventilation, then brush the tops of each pastry with the remaining plant-based milk. Bake in the middle rack of the oven for 20 to 22 minutes, until the pasty is golden brown. Remove from the oven and let cool slightly on the baking sheet.: Before the pastries go in, cut 1 to 2 small slits on top to vent steam, then brush the tops with the remaining plant based milk for a golden finish. As they bake on the middle rack, the oven surrenders a warm aroma of browned pastry and caramelized apples . Look for a deep golden brown color and pronounced separation of layers as confirmation that the pastry is cooked through, usually about 20 to 22 minutes at 400 F. If the tops brown too quickly, tent with foil to avoid burning while the centers finish cooking.
Make the Glaze (optional): Add the powdered sugar to a medium bowl and add 1 tablespoon of milk; mix well. If the mixture is too thick, add more milk in 1/2 teaspoon increments, until the glaze reaches your desired thickness.: The powdered sugar and non dairy milk should blend into a smooth, glossy glaze that drapes over the turnovers. Start with one tablespoon of milk and add in 1/2 teaspoon increments to reach a ribbon like consistency that holds its shape briefly on a spoon. If the glaze is too runny it will slide off instead of coating, if too thick it will clump and not drizzle evenly. Sift powdered sugar first to avoid lumps for a silky finish.
Glaze & Serve: Drizzle the glaze over the turnovers, then serve warm; leftovers will keep at room temperature for up to 3 days or can be frozen for up to 2 months. Reheat leftovers in the oven or toaster oven.: Drizzling the glaze over slightly warm turnovers lets it set into a thin sheen rather than a wet puddle, adding a sweet, tactile contrast to the flaky crust. Serve warm to enjoy the ideal mix of crisp pastry and tender, aromatic filling. Leftovers keep at room temperature for up to 3 days or can be frozen; reheat in an oven or toaster oven to re crisp the layers. Avoid microwaving, which makes the pastry soft and chewy instead of flaky.