Peel the apple and cut into 8 wedges, then into 2-3 mm slices. Coat them with granulated sugar. Cover with plastic wrap and microwave for 3 minutes. Let it cool down.
Combine the cake flour and baking powder to sift.
Combine the roughly crushed walnuts with the melted butter and blend them together. Chill in the fridge for later use.
Beat the egg in a bowl. Add the granulated sugar, vegetable oil, and milk in order. Mix with each addition.
Into the same bowl, add the sifted powdered ingredients from Step 2 and fold in with a rubber spatula. Then add the apple from Step 1 with its juice.
Pour the dough into the pound tin. (It's rather soft, but don't worry.)
Gently place the walnuts from Step 3 on top. Don't worry if they sink a bit.
Bake in the bottom rack of your oven for 40 minutes at 180℃ (take a peek after 30 minutes; cover it with aluminum foil if they seem like they're going to burn). Let it cool down slightly before removing from the pound cake tin.
Story Behind this Recipe
Using "Cinnamon and Walnut Cake" (Recipe ID: 185725) as a base recipe, I mixed some apples into the dough. I've posted this recipe after adjusting the measurements.
For best results, use bread knives to cut the cake into slices. I think this cake would also be amazing with persimmons.