In a large mixing bowl, cream together the softened butter and the sugar. Add eggs one at a time, beating well after each addition. Stir in vanilla extract, milk, and Greek yogurt.
Add the yellow cake mix and flour to the creamed mixture. Mix until well combined, ensuring there are no lumps.
Grease and flour a 10-inch Bundt pan. Pour the batter into the prepared Bundt pan. Smooth the top with a spatula.
Bake in the preheated oven for 60-70 minutes, or until a toothpick inserted into the center comes out clean. If needed, cover the cake during the last 20 minutes of baking to prevent over-browning.
Allow the cake to cool in the pan for 10 minutes before inverting onto a wire rack to cool completely. Serve as desired.