Preheat the oven to 350°F (175°C) and grease a 9-inch round cake pan until it feels slick to the touch.

Whisk flour, baking powder, baking soda, cinnamon, nutmeg, and salt in a medium bowl until uniform, pale tan, and fragrant.

Beat butter and granulated sugar in a large bowl with an electric mixer for 3 minutes until light, fluffy, pale yellow, and creamy.

Add eggs one at a time, beating well until the batter is glossy, smooth, and makes a soft slapping sound.

Incorporate vanilla, then alternate adding dry ingredients and buttermilk in three parts, mixing on low just until combined to a thick, creamy, soft golden tan consistency.

Gently fold in diced apples with a rubber spatula until evenly distributed, creating a chunky, textured batter with the scent of fresh apples and cinnamon.

Pour batter into the prepared pan and smooth the top with a spatula, noting the uneven surface and visible air pockets.

Bake for 35-40 minutes until the cake is golden brown, edges have pulled away, and a toothpick comes out clean amidst a sweet apple aroma.

Cool in the pan for 10 minutes, then invert onto a wire rack with a soft thump, revealing the caramelized bottom crust.

Whisk powdered sugar, milk, and vanilla in a small bowl until the glaze is smooth, shiny, white, and pourable.

Drizzle glaze over the completely cooled cake, allowing it to pool on the sides, and sprinkle with pecans if desired.

Slice and serve to enjoy the moist, tender texture and spiced apple bursts.