Preheat oven to 350°F (175°C). Grease a 10×15-inch jelly roll pan well.

In a large bowl, cream the softened butter and sugar until light and fluffy. Beat in the eggs and vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt.

Alternate adding the dry ingredients and sour cream (or buttermilk) to the creamed mixture, stirring just until combined. Do not overmix.

Spread about ⅔ of the batter evenly into the prepared pan. Dollop the pie filling over the batter. Drop the remaining batter by spoonfuls on top. Gently swirl with a knife, leaving distinct pockets of fruit.

Bake for 35–40 minutes until golden brown and a toothpick inserted near the edge comes out clean.

Cool completely in the pan. Whisk glaze ingredients until smooth and drizzle over the cooled cake.