• Preheat the oven to 350 °F.
• Line a 9" x 13" baking pan with a piece of parchment paper or alternatively spray the pan with baking spray.
• In a medium mixing bowl, stir together the flour, 1 tablespoon cinnamon, nutmeg, baking soda, and salt. Set aside.
• In a large mixing bowl, stir together the brown sugar, granulated sugar, oil, eggs and vanilla until thoroughly combined.
• Add in the flour mixture and mix just until well combined.
• Place the apples in a small bowl and sprinkle the remaining 1 tablespoon granulated sugar and 1 teaspoon ground cinnamon over the apples. Stir to coat the apples in the cinnamon sugar. Fold the apples into the batter.
• Pour the batter into the prepared pan and bake for 33-40 minutes or until a toothpick inserted in the center comes out clean.
• Let cool completely before frosting.

Make the frosting:

• Melt the butter in a medium saucepan over medium heat.
• Stir in the brown sugar and whipping cream. Once the mixture starts bubbling, stop stirring.
• Let the mixture come to a full boil and boil for 1 minute without stirring. Remove the pan from the heat.
• Stir in the vanilla, 1/4 teaspoon salt, and gradually add the powdered sugar.
• Whisk until the powdered sugar is fully incorporated and no lumps of sugar remain. Frosting will get thicker as it starts to cool, but will still seem more like a sauce than a traditional frosting.
• Add the remaining 1/4 teaspoon salt, if desired.
• Once the cake has cooled, pour the frosting over the top. Let the frosting cool completely before serving.
• Refrigerate any leftovers for up to 4 days. Let come to room temperature before serving.