Prepare the Topping: In a skillet over medium heat, melt the vegan butter or coconut oil. Stir in the brown sugar and cinnamon until combined. Add the apple slices and cook for about 5-7 minutes, or until the apples are slightly softened and caramelized. Remove from heat and set aside.
Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan.
Arrange the Apples: Pour the caramelized apple mixture into the bottom of the prepared cake pan, spreading it evenly.
Make the Cake Batter: In a large mixing bowl, combine the flour, sugar, baking powder, baking soda, salt, and cinnamon. In another bowl, mix together the almond milk, vegetable oil, apple cider vinegar, and vanilla extract.
Combine Wet and Dry Ingredients: Pour the wet ingredients into the dry ingredients and mix until just combined. Be careful not to overmix; a few lumps are okay.
Pour the Batter: Gently pour the cake batter over the arranged apples in the cake pan, spreading it evenly.
Bake: Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Cool and Serve: Allow the cake to cool in the pan for about 10 minutes, then carefully invert it onto a serving plate. Let it cool slightly before slicing and serving.