Preheat your oven to 350°F (180°C) then butter and line a 9-inch bake pan. Set aside.

In a medium bowl, combine the flour, oats, sugar, and salt. Next rub in the cold butter until fully incorporated and you've reached the texture of coarse breadcrumbs. Set aside in the fridge while you make the cake.

Cream the butter and the sugar together in a large bowl until light and fluffy.

Next, add in the vanilla then beat in the eggs one at a time.

In a separate medium bowl combine the flour, baking powder cinnamon, and salt.

Fold the dry ingredients into the wet along with the milk.

Once the batter has formed, transfer it to the prepared cake pan and lay on the sliced apples, making sure they are arranged in one even layer.

Cover the apples with all the streusel topping.

Bake for roughly 65-75 minutes, or until the top is golden brown all over and crisp.

Remove from the oven and allow cooling slightly before turning out of the tin.

When ready to serve, dust the cake with powdered sugar, slice and enjoy. Store the cake in an airtight container at room temperature for up to 4 days.