Preheat the oven to 350°F (177°C) and line two standard muffin tins with cupcake liners.

In a large bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until well combined. Set this mixture aside. Open the can of crushed pineapple, draining and reserving 2 tablespoons of juice specifically for the buttercream later.

In the bowl of a stand mixer or using a handheld electric mixer, beat the softened butter and granulated sugar on medium speed until light and fluffy, about 2 to 3 minutes. Add the eggs one at a time, beating well after each addition to ensure a smooth, cohesive batter. Stir in the vanilla extract.

With the mixer on low speed, alternately add the dry ingredients with the sour cream and milk, beginning and ending with the flour mixture. Mix until just combined, taking care not to overwork the batter. Gently fold in the crushed pineapple until evenly distributed throughout.

Scoop the batter into the prepared cupcake liners, filling each about two-thirds full for a perfect rise. Bake in the preheated oven for 18 to 21 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Remove from the oven and allow the cupcakes to cool in the pan for 5 minutes. Then transfer them to a wire rack to cool completely before frosting.

For the buttercream, beat the softened butter and vegetable shortening together in a large bowl on medium speed until creamy and pale, about 1 minute. Add the vanilla extract and mix until incorporated.

Gradually add the sifted confectioners’ sugar, one cup at a time, starting on low speed to prevent a sugar cloud, and increasing to medium speed once incorporated. Scrape the sides and bottom of the bowl occasionally to ensure even mixing. When the sugar is fully incorporated, the frosting will initially look dry.

Pour in the reserved pineapple juice and beat the mixture until it becomes light, fluffy, and spreadable.

Once the cupcakes are completely cool, pipe or generously spread the pineapple buttercream on top. Garnish with fresh pineapple wedges or leaves for a decorative, tropical flair, if desired.