
Preheat oven to 350°F (175°C). Grease and flour your loaf pan or line it with parchment paper if desired.
In a medium bowl, whisk together the flour, baking powder, nutmeg, and salt. Set aside.
Cream butter and sugar in a large mixing bowl with an electric mixer on medium for about 6 minutes, until light and fluffy.
Add one egg at a time, beating well after each one.
Mix in the buttermilk and vanilla extract until well combined, then gradually add the flour mixture in two parts, mixing gently until just combined. Be careful not to overmix.
Gently fold in the drained crushed pineapple and rum (if using) until evenly distributed.
Pour the batter into the prepared loaf pan.
Bake in the preheated oven for 45-55 minutes or until a toothpick inserted into the center comes out clean. If the top starts browning too quickly, cover it loosely with aluminum foil.
Cool the bread in the pan for about 10 minutes. Then, transfer it to a wire rack to cool completely.
Whisk the powdered sugar and reserved pineapple juice in a small bowl until smooth.
Once the bread has completely cooled, spread the glaze evenly over the top and serve.