Preheat oven to 350°F. Grease a 9x13-inch baking dish.

Make the cake batter by whisking together flour, sugar, baking powder, and salt. In a separate bowl, beat eggs, milk, and melted butter.

Add wet ingredients to dry and stir until just combined. Fold in diced apples.

Spread the batter in your pan. Mix brown sugar, cinnamon, and melted butter. Drop spoonfuls over the batter, then swirl with a knife or spatula.

Bake 28–32 minutes, or until a toothpick comes out clean and the cake is golden.

Whisk powdered sugar, milk, and vanilla until smooth. Drizzle generously over the warm cake.

Serve & enjoy warm for the full effect, and don’t skip leftovers—they’re just as good the next day.