Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan or line with parchment paper, leaving an overhang on the long sides.
Measure all ingredients and allow refrigerated items to come to room temperature.
Peel and grate the apples using the large holes of a box grater. Gently press the grated apples between paper towels to remove excess moisture.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt.
In a large bowl using an electric mixer, beat the softened butter on medium speed for 1 minute until creamy. Add both sugars and beat for 3-4 minutes until the mixture becomes lighter in color and fluffy in texture.
Beat in the eggs one at a time, allowing each to fully incorporate before adding the next. Scrape down the sides of the bowl as needed. Mix in the vanilla extract and sour cream until just combined.
Gradually fold the dry ingredients into the wet mixture using a rubber spatula, mixing just until no flour streaks remain.
Gently fold in the grated apples, distributing them evenly throughout the batter.
Pour the batter into your prepared loaf pan and smooth the top with a spatula. Bake in the preheated oven for 60-65 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (but no wet batter).
Allow the cake to cool in the pan for 15 minutes, then carefully remove to a wire rack to cool completely.
For the optional glaze, whisk together the powdered sugar, apple cider or milk, vanilla extract, and cinnamon until smooth. Drizzle over the cooled cake.