Preheat the Oven: Preheat your oven to 350°F (175°C) and grease a cake pan.
Mix Dry Ingredients: In a bowl, whisk together the all-purpose flour and baking powder. Set aside.
Cream Butter and Sugar: In a separate mixing bowl, cream the softened butter, shortening, and granulated sugar together until the mixture is light and fluffy.
Add Eggs: Beat in the eggs one at a time, ensuring each one is fully incorporated.
Combine Wet Ingredients: Stir in buttermilk, crushed pineapple, and vanilla extract until everything is well mixed.
Combine Mixtures: Gradually add the dry ingredients to the wet mixture, mixing until just combined and no flour streaks remain.
Pour into Pan: Pour the batter into the prepared cake pan, ensuring it is spread evenly.
Bake: Bake in the preheated oven for about 35-40 minutes, or until a toothpick inserted in the center comes out clean.
Cool the Cake: Allow the cake to cool completely in the pan.
Prepare the Glaze: Use the reserved pineapple juice to create a simple glaze by mixing it with powdered sugar to your desired consistency.
Finish with Glaze: Drizzle the glaze over the cooled cake, slice, and serve!