Preheat your oven to 325°F.
Using a hand mixer, combine all the vanilla cake ingredients in a medium mixing bowl until well combined.
1 Betty Crocker white cake mix, 4 eggs, 1 cup sour cream, ¾ cup avocado or other neutral vegetable oil, 1 tbsp vanilla extract
Pour approximately ⅔ of the cake batter into a sprayed 9 x 13 pan. Set the remaining ⅓ aside.
Mix the brown sugar and cinnamon in a separate bowl.
⅓ cup brown sugar, 1½ tsp ground cinnamon
Sprinkle the cinnamon sugar over the cake batter in an even layer. Then pour the remaining ⅓ of the cake batter over the cinnamon sugar layer.
Lightly swirl the cinnamon sugar into the cake batter using a knife or kitchen skewer.
Bake the cake for 32-35 minutes at 325°F, or until the top of the cake is golden and a toothpick comes out clean when inserted into the cake.
Remove the cake from the oven and place the pan on a wire cooling rack. While the cake is cooling, prep your simple glaze.