First, preheat your oven to 325°F. Grab a 9-inch bundt cake pan, give it a good spray with nonstick cooking spray, and set it aside for later.
In a medium-sized bowl, go ahead and mix together the flour and baking powder. Then, set that aside too.
Now, in a standing mixer or a large mixing bowl, cream the butter, shortening, and sugar until they're all nice and cozy together.
Add those eggs one at a time, giving each one a good 30-second beating on high speed.
Time for a lil' dance between the flour mixture and buttermilk – add them to the mix, alternating between the two and stirring just a bit in between.
Next, toss in the pineapple and vanilla extract, and give it a gentle beat until everything's evenly combined.
Pour that lovely batter into your prepared bundt pan and bake it for 75-85 minutes. You'll know it's done when a toothpick comes out with just a few moist crumbs. Let it cool for 10 minutes, then flip it out onto a wire rack to cool completely.
Finally, whisk up all those glaze ingredients until smooth as silk, and drizzle it right over the top of your cooled cake.