Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan or line it with parchment paper.
In a large mixing bowl, whisk together all the dry ingredients: the flour, sugar, baking powder, baking soda, cinnamon, nutmeg, and salt.
In another bowl, add all the wet ingredients: the melted vegan butter, applesauce, plant-based milk, apple cider vinegar and vanilla extract until well combined. Mix and combine well.
Add the dry ingredients to the wet ingredients. Stir until well combined. The batter will be thick. Don't over mix!
Gently fold in the diced apples until evenly distributed throughout the batter.
Transfer the batter to the prepared cake pan and spread it out evenly. IF using the optinal sugar top crust, evenly sprinkle the 2 tablespoons of coarse granulated sugar over the top of the unbaked batter now.
Bake in the preheated oven for 50 minutes to an hour, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and let it cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
If you did not use the coarse sugar topping before baking, you can dust the top of the completely cooled cake with powdered sugar, if desired.
Slice and serve the Vegan Irish Apple Cake as is or with a dollop of vegan whipped cream or dairy-free ice cream.