Peel, core, and slice apples. Place in a large mixing bowl.
Mix 2/3 cup sugar with 1 1/2 teaspoons of cinnamon in a small bowl.
Pour cinnamon sugar mixture over apples and stir until well combined.
Place apples in a 9x13 inch baking dish that has been lightly greased with butter.
In a large bowl, mix flour, 1 cup sugar, egg, baking powder, 1/2 teaspoon cinnamon, and salt. Mix with a fork until it resembles coarse crumbs.
Sprinkle evenly over the apples.
Melt the butter and drizzle over the apple crumb mixture.
Bake in a preheated 350-degree oven for 45-55 minutes until bubbly and golden brown.
Serve warm with vanilla ice cream (not included in nutrition information)