Preheat the oven to 350°F and spray a 9x13-inch baking dish with nonstick cooking spray. Set aside.
In a medium mixing bowl, combine 2 cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon ground cinnamon, 1/2 teaspoon ground nutmeg and 1/2 teaspoon salt. Whisk until evenly blended. Set aside.
In a large bowl, stir together 3/4 cup vegetable oil, 1 cup granulated sugar, 1/2 cup light brown sugar and 1 teaspoon vanilla extract until smooth. Add 2 large eggs, one at a time, mixing well after each addition.
Gradually incorporate the dry ingredients into the wet mixture, stirring just until combined. Gently fold in 3 cups peeled, cored, and diced (about ½ inch thick) apples.
Spread the batter evenly into the prepared baking dish. Bake on the middle oven rack for 45-50 minutes, or until a toothpick inserted into the center comes out clean. Note: Oven times can vary and many ovens have hot spots. Please go by doneness and not strictly by time.
Let the cake cool for 10-15 minutes after baking. While the cake cools, make the icing.
While the cake cools, prepare the icing. In a small saucepan over medium heat, melt 1/4 cup unsalted butter. Add 1/2 cup light brown sugar, 1/4 cup granulated sugar and 1/4 cup heavy cream, whisking constantly. Bring the mixture to a gentle boil and cook for 2-3 minutes until it thickens slightly. Remove from heat and whisk in 1/2 teaspoon vanilla extract.
Pour the icing evenly over the still slightly warm cake, spreading it gently if needed.
Allow the cake to finish cooling completely before cutting into slices and serving. Enjoy!
Notes
Please refer to my FAQ’s (Frequently Asked Questions) and ingredient list above for other substitutions or for the answers to the most common questions.