01 -
Preheat the oven to 350ºF (175ºC).
02 -
In a large bowl, mix the egg, brown sugar, applesauce, and vanilla extract together. Add almond milk, apple cider vinegar, and avocado oil, and stir to combine.
03 -
In a separate bowl, whisk together the all-purpose flour and baking soda.
04 -
Gradually fold the dry ingredients into the wet mixture until just combined. Gently fold in the chopped apples.
05 -
Line a 9×13-inch baking pan with parchment paper. Pour the batter into the pan and smooth the surface.
06 -
In a medium bowl, mix the softened butter, cinnamon, walnuts, granulated sugar, and nutmeg (if using). Spread this mixture evenly over the apple cake batter.
07 -
Place the pan on the middle oven rack and bake for 30-40 minutes, or until a toothpick inserted into the center comes out clean.
08 -
Let the cake cool before slicing. Optionally, drizzle the icing over the cake, or serve as is.