In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
In a separate bowl, combine the milk, sour cream, reserved pineapple juice, and vanilla extract. Mix until smooth.
Using a third bowl, cream the softened butter with the granulated sugar. Beat with a handheld mixer on speed 7 for approximately 2 minutes until light and fluffy.
Add the eggs one at a time, beating for about 20 seconds after each addition until fully incorporated.
Begin combining the dry and wet mixtures into the butter base. Start by folding in one-third of the flour mixture using a rubber spatula. Then add half of the milk mixture and fold gently. Continue by incorporating another third of the flour mixture, followed by the rest of the milk mixture, and finally the remaining flour. Fold in the chopped leftover pineapple.
Gently spoon the finished batter into the prepared cake pan, spreading it evenly over the arranged fruit and smoothing the top.
Bake uncovered for 30 minutes. Then, loosely cover the cake with foil and return to the oven for an additional 15 minutes, or until a skewer inserted into the center comes out clean.