Preheat oven to 350 degrees F (180 degrees C). Peel Granny Smith Apple (4).
Prepare a large bowl of water. Squeeze a Lemon (1/2) in the water, adding the lemon in the water as well.
Slice apples, put all the apples back in the acidulated water and set aside.
To make the topping, combine All-Purpose Flour (1/2 cup), Granulated Sugar (1/4 cup), Brown Sugar (1/4 cup), Oats (1 cup) and Salt (1 pinch) in a bowl.
Grate the Butter (1/2 cup) and add it in. Use your hands to mix butter into the dry ingredients until it has a crumbly texture.
Drain the apples and add Ground Cinnamon (1 teaspoon), Salt (1 pinch), Corn Starch (1 teaspoon), Vanilla Extract (1 dash), any remaining sugar and the juice from the lemon.
Mix well until the apples are coating with the ingredients. The juices from the apple will create a beautiful glossy syrup.
Add apples to a baking pan and top with the crumble mixture.
Place in the oven for 20 to 25 minutes.
Once the top is nice and golden, let it sit for about 10 minutes.
Serve with ice cream and enjoy!