Preheat the oven to 350 °F. Grease and flour a 9x13 baking dish.
Cinnamon Pecan Filling
Combine the brown sugar with the chopped pecans and cinnamon together in a small bowl. Set aside.
Cake
Combine the cake mix, oil, eggs, and sour cream in the bowl of an electric mixer. Mix on low speed for 30 seconds and then medium speed for 2 minutes, scraping down the sides as needed.
Pour half of the cake batter into the prepared pan. Spoon the Cinnamon Pecan Filling over the cake batter. Carefully spread the remaining cake batter over the filling.
Bake for 45 minutes or until deep golden brown. Remove from the oven and cool for 5 minutes.
Cake Glaze
Combine the powdered sugar, milk, and vanilla. Add additional milk if the glaze needs thinning. Spread over the warm cake. Cool completely and serve.
This recipe was calculated using the exact brands and measurements I used to make this recipe. If you are following a strict diet please note changing anything will cause the nutritional info to change. My calculations are intended as a guide only.