Preheat the oven to 190C. Grease and flour muffin pans, or line with paper liners.
In a large bowl, stir together 2 cups flour, white sugar, baking powder and salt. Drain pineapple, reserving 1/4 cup juice. Make a well in the center of the dry ingredients, and pour in the reserved juice, egg, milk, and 1/4 cup melted butter. Fold into mixture.
Spoon batter into muffin cups, then spoon crushed pineapple over the batter.
Bake for about 20 - 30 minutes in the preheated oven, until a toothpick inserted in the crown of the muffin comes out clean.