Prepare the Apples: Peel and dice the apples into small, bite-sized pieces. Add them to a bowl with the brown sugar and cinnamon, then toss until evenly coated. Set aside while preparing the batter.
Make the Batter: Preheat the oven to 350°F (175°C). Grease a 9 x 5-inch loaf pan and line it with parchment paper. Whisk together the flour, baking powder, and salt in a mixing bowl. In a separate bowl, beat the softened butter and granulated sugar until light and creamy. Add the eggs one at a time, then mix in the milk and vanilla. Gradually add the dry ingredients to the wet ingredients. Mix just until combined. Do not overmix.
Layer the Bread: Spread about half of the batter into the prepared loaf pan. Add about half of the cinnamon-coated apples over the batter. Spoon the remaining batter over the apples, then add the remaining apples on top. Use a knife to gently swirl the apples through the batter.
Bake: Bake for approximately 50–60 minutes, or until the loaf is golden brown and a toothpick inserted into the center comes out mostly clean. If the top begins browning too quickly, loosely cover the loaf with aluminum foil during the final part of baking.
Cool: Allow the bread to cool in the pan for about 10–15 minutes. Carefully remove it from the pan and transfer it to a wire rack. Let it cool substantially before adding the glaze.
Make the Glaze: Whisk the powdered sugar, milk, and vanilla extract together until smooth. Add a tiny amount of additional milk if needed to reach a smooth drizzling consistency.
Glaze the Bread: Drizzle the glaze over the cooled Apple Fritter Bread. Allow the glaze to sit for several minutes before slicing.
Serve: Slice the bread with a serrated knife and serve slightly warm or at room temperature.