Preheat oven to 350°F degrees. Butter an 8×8 baking dish, and set aside.
Chop the six Granny Smith apples (approximately 4 cups of chopped apples).
Add the chopped apples to a mixing bowl and sprinkle them with the granulated sugar, 1 teaspoon of ground cinnamon, 2 tablespoons of brown sugar, and lemon juice.
Stir the apples to coat them well with the cinnamon mixture.
Pour the apples into the prepared baking dish.
In a medium-sized bowl, combine the oats, 1 cup of brown sugar, the remaining ground cinnamon, all-purpose flour, and salt. Stir to combine well.
Using a pastry cutter or two forks, cut the cold butter pieces into the oat mixture. Cut the butter into the mixture until the pieces are small and crumbly. Make sure all of the flour and oat mixture is moistened.
Sprinkle the crumb mixture on top of the apples evenly.
Bake in the preheated oven for 45-50 minutes or until the top of the crisp is golden brown.
Serve warm with a scoop of ice cream if desired.
Notes
Granny Smith, Golden Delicious, and Honey Crisp apples are good varieties for baking.