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, cream together the softened butter and granulated sugar until light and fluffy.

Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.

In another bowl, whisk together the flour, baking powder, salt, ground cinnamon, and nutmeg (if using).

Gradually add the dry ingredients to the wet mixture, alternating with the milk. Begin and end with the flour mixture, mixing until just combined. Avoid overmixing.

Gently fold in the diced apples until evenly distributed throughout the batter.

Pour the batter into the prepared cake pan, smoothing the top with a spatula.

In a small bowl, mix the brown sugar with a pinch of cinnamon. Sprinkle this mixture evenly over the top of the batter.

Bake in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.

Slice and serve the Cinnamon Apple Teacake warm or at room temperature, either plain or with a dusting of powdered sugar.