Preheat your oven to 350°F (175°C). Grease and line a 9x5-inch loaf pan with parchment paper.

In a large bowl, cream the softened butter and granulated sugar until pale and fluffy. Beat in the eggs one at a time, then add the vanilla extract.

Gently fold in the all-purpose flour and baking powder, alternating with the buttermilk. Mix only until the flour disappears.

Toss the diced apples with 2 tbsp granulated sugar and 1 tsp cinnamon. In a separate small bowl, mix the light brown sugar and remaining 1 tsp cinnamon for the swirl.

Spread half the batter into the loaf pan. Top with half the apples, then sprinkle with half the brown sugar swirl mixture. Repeat with the remaining batter, apples, and swirl mixture.

Insert a butter knife into the batter and swirl in a figure-eight motion. Bake for 55-65 minutes until the crust is deep golden-brown and a toothpick comes out clean.

Cool the bread slightly. Whisk the powdered sugar and heavy cream to create a thick opaque white glaze. Pour over the loaf, allowing it to drip down the edges. Slice and serve.