Preheat your oven to 350℉, then grease and flour a 10-inch bundt pan. Set the prepared pan aside.

In a large mixing bowl, cream together the softened butter and sugar using an electric mixer until the mixture is light and fluffy. Be sure to scrape down the sides of the bowl to ensure even blending.

Add the eggs one at a time, mixing on low speed after each addition.

Stir in the vanilla extract and mix well.

Incorporate the sour cream and milk into the batter, mixing thoroughly.

Gradually add the flour and yellow cake mix, blending until the batter is smooth and well combined.

Pour the batter into the prepared bundt pan, spreading it evenly. Bake for approximately 70 minutes.

Check the cake after about 40 minutes. If the top is browning too quickly, cover it loosely with foil and continue baking. The cake is done when a toothpick inserted into the center comes out clean.

Allow the cake to cool in the pan for 10 minutes, then invert it onto a wire rack or serving tray. Slice and enjoy!