Preheat your oven to 350°F (175°C) and grease a 9×13 inch baking pan.
To make the crumb topping, combine flour, brown sugar, cinnamon, and salt in a bowl. Cut in the cold butter until the mixture resembles coarse crumbs, then set aside.
In a large bowl, whisk together flour, baking powder, cinnamon, and salt for the cake batter.
In a separate bowl, cream together the softened butter, light brown sugar, and granulated sugar until fluffy.
Beat in the eggs one at a time, followed by the vanilla extract.
Gradually add the dry ingredients to the wet mixture, alternating with the milk, mixing until just combined.
Fold in the chopped apples and pecans.
Spread the batter evenly into the prepared pan.
Sprinkle the crumb topping generously over the cake batter.
Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
Allow to cool before whisking the confectioners sugar and milk together to create a glaze, then drizzle over the cooled cake.