Whisk together in a medium mixing bowl, flour (3 cups), baking powder (1/2 teaspoon), and salt (1/2 teaspoon); set aside.
Preheat oven to 325°F (163°C). Grease and flour a 12-cup bundt pan.
In the bowl of a stand-up mixer, beat butter (1 1/2 cups) on medium speed, until light and fluff, 6 minutes.
Gradually mix in sugar (3 cups) until blended. Beat on medium for 1 additional minute.
Add eggs (5 large), one at a time, mixing after each addition just until the yolk disappears.
Reduce mixer speed to low. Add flour mixture and buttermilk (1 cup), beginning and ending with flour mixture, on low speed until just combined. Scrape down the bowl as needed. Mix in vanilla (1 tablespoon). Gently fold in drained pineapple (1 can).
Pour batter into the prepared bundt pan. Tap the pan on the counter to remove any air bubbles.
Bake for 45 minutes in the preheated oven. Cover with foil and continue to bake, about 45 minutes longer, or until a wooden skewer inserted into the center comes out with just a few moist crumbs. Cool in a pan on a wire rack for 1 hour. Remove from the pan and cool completely on a wire rack.
Make Glaze:
In a large 2-cup liquid measuring cup add confectioners' sugar (2 cups), melted butter (2 tablespoons), and vanilla (1 teaspoon). Whisk in 2 tablespoons of milk. Add more milk, as necessary, until you achieve a very thick pourable consistency. Drizzle over the top of the cooled cake.
Add pineapple tidbits to the top just before serving.
Notes
Pineapple Tidbits: I suggest you only add the pineapple tidbit to the top of the cake right before serving. Even if you drain it well and dry it on paper towels, there will be some juice that will drip out. The enzyme in it can break the glaze.
Over Beating: Yes, you still beat the butter for 6-7 minutes. Once the eggs are added is when you need to be careful not to overbeat! You just beat the eggs until the yolks disappear.
Baking: You might notice this pound cake is baked at a lower temperature than some recipes. We’re looking for a slow and steady bake to produce its velvety texture.
Room Temperature Ingredients: It’s best if all the ingredients are at room temperature when you mix up the batter.