Prep & Preheat: Preheat your oven to 350°F (175°C). Grease an 8.5x4.5-inch metal loaf pan with butter and line with parchment paper, leaving an overhang on the sides for easy lifting.

Mix Dry Ingredients: In a medium bowl, whisk together all-purpose flour, baking powder, baking soda, ground cinnamon, nutmeg, and fine sea salt until well blended. In a small ramekin, toss 1 tablespoon of this flour mixture with the diced apple chunks (this keeps the apples suspended evenly throughout the bread so they do not sink to the bottom).

Cream Wet Ingredients: In a large bowl or stand mixer, beat the softened butter, brown sugar, and granulated sugar for 2 minutes on medium speed until fluffy and light. Add eggs one at a time, beating well after each, then stir in vanilla extract.

Combine Batter: With the mixer on low speed, alternately add the flour mixture and milk in two batches, mixing just until combined. Gently fold in the diced apple chunks with a silicone spatula.

Layer & Swirl: Mix the cinnamon swirl ingredients (brown sugar and cinnamon) in a small dish. Spread half of the apple batter into the prepared loaf pan. Scatter half of the cinnamon swirl mixture over the top. Layer the remaining batter over, then top with the remaining cinnamon swirl. Use a butter knife to gently swirl the top layer in figure-eight motions.

Bake to Golden: Bake for 50 to 55 minutes, or until a wooden toothpick inserted into the center comes out clean with just a few moist crumbs (tent loosely with foil after 35 minutes if the top is browning too quickly). Let cool in the pan for 15 minutes, then lift out onto a wire cooling rack to cool completely.

Glaze & Slice: In a small bowl, whisk powdered sugar, pure maple syrup, heavy cream, and flaky sea salt until smooth and pourable. Drizzle generously over the cooled loaf. Allow the glaze to set for 10 minutes before slicing into thick, tender pieces.