Preheat oven to 350 F. Spray a springform pan with non stick spray.
Slice the apples ¾ of the way through, leaving the base attached. Toss apples the lemon juice.
In the bowl of an electric mixer, beat butter and sugar until light and creamy.
Add vanilla extract and lemon zest. Mix until combined.
Add eggs one at a time, mixing well after each addition.
In a medium bowl, combine salt, flour and baking powder. Mix to combine.
Add dry ingredients to batter in 2 batches, mixing well after each addition.
Add milk and mix until thoroughly combined.
Transfer batter to prepared pan and spread in an even layer.
Place apples on top of the batter, pressing slightly into the batter.
Sprinkle demarara sugar on top.
Bake for 45 minutes, until a tester inserted comes out clean.
Cool in the pan for 10 minutes.
Remove the outer shell of the springform pan.
Garnish with powdered sugar on top, if desired.