Grease and flour a tube pan.(We used a pan with 12 cup baking capacity.)
Lower the oven rack to the next to lowest position so that the cake will sit in approximately in the center of your oven. Preheat oven to 325 degrees F.
In a separate bowl whisk the flour and baking powder to combine, set aside for later.
Mix the butter with the paddle attachment in your mixer, mixing until smooth. Next, add the peanut butter, mixing until smooth.
Next, gradually add the white and brown sugar and mix on Medium Speed until light and fluffy for 4-5 minutes.
Add the eggs one at a time blending after each to incorporate.
Add the vanilla extract to the milk.
Add the flour mixture alternately with the milk to the butter, sugar, egg mixture. Begin and end with the dry ingredients. I add the dry 3 times and milk twice.
Bake at 325 degrees for 1 hour and 10 minutes or until a toothpick comes out clean. **Baking times may vary! It may take a bit longer, peek in as you approach the end time and adjust as needed.
This makes approximately 8 cups of batter.
Allow to cool in the pan for about 10 minutes before flipping out onto wire rack.