Heat the oven to 350°F (175°C) and thoroughly grease a standard 6- or 12-cavity doughnut pan. Make sure the sides and center posts are coated so the baked doughnuts release easily.

Whisk the flour, granulated sugar, baking powder, baking soda, and salt together in a medium bowl. In a separate bowl, whisk the egg, very well-drained crushed pineapple, milk, melted butter, and vanilla.

Add the wet mixture to the dry ingredients and stir only until combined. A few small lumps are fine, so avoid mixing longer than necessary.

Spoon or pipe the batter into the prepared pan, filling each cavity about two-thirds full. Do not overfill, because excess batter can cause the center holes to close while the doughnuts bake.

Bake for 10 to 12 minutes, until the doughnuts spring back lightly when pressed and a toothpick inserted into the thickest part comes out clean. Let them cool in the pan for about 5 minutes before transferring them to a rack.

Stir the confectioners’ sugar with 2 to 3 tablespoons of pineapple juice or milk, adding the liquid gradually until the glaze is thick but pourable. Stir in the optional vanilla, then dip or drizzle the glaze over the cooled doughnuts.