Preheat oven to 350 degrees Fahrenheit. Spray a 9 x 13 x 1-inch baking sheet with nonstick cooking spray, then lightly dust with flour. Tap out the excess flour and set aside.
In a large bowl, combine 4 cups chopped Granny Smith apples and 2 cups granulated sugar. Stir in ½ cup vegetable oil, 2 lightly beaten eggs, and 1 teaspoon vanilla extract.
In a medium bowl combine 2 cups all-purpose flour, 2 teaspoons baking powder½ teaspoon baking soda, 2 teaspoons ground cinnamon, ½ teaspoon ground nutmeg, and 1 teaspoon salt.
Add the flour mixture to the apple mixture and mix to combine. Add ½ cup milk and stir until just combined. Add 1 cup roughly chopped pecans and stir until combined.
Pour the batter into the prepared pan and bake for 30-40 minutes or until a toothpick comes out clean from the center. Let the cake cool completely.
Brown Sugar Cream Cheese Frosting
Add 8 ounces room temperature cream cheese to a large bowl and beat with a hand mixer on high speed until smooth. Add ¼ cup softened salted butter and beat until smooth, scraping down the sides and bottom of the bowl to ensure it is incorporated evenly.
Add 2 teaspoon vanilla extract and 1 cup light brown sugar. Beat for 5 minutes on medium-high speed, until it is light and fluffy and the sugar has dissolved.
Spread the frosting evenly on top of the cooled cake. Refrigerate until serving.