Preheat the oven to 180 degrees Celsius. Grease a medium-size round pan with butter.
In the bowl of a stand mixer, beat together the vegetable oil, sugar, and
vanilla until fluffy, about 2 minutes. Add the eggs, one at a time,
until fully incorporated. Add the cognac, beating until smooth.
Add the flour, baking powder, apple pie spice, and salt
and mix on low speed until just combined, being sure the batter is
completely mixed.
Add the sliced apples into the cake batter and fold them in the batter using silicone or wooden spatula.
Spoon the cake batter into the prepared pan. Transfer to the oven and bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean. If the top of the cake is browning, cover with foil for the last 15 minutes of baking.
Let cool 10 minutes and then invert the cake onto a plate. Sprinkle the cake top with powder sugar and serve warm or at room temperature.