Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large bowl, cream butter and sugar until light and fluffy (2–3 minutes).
Beat in egg and vanilla until smooth.
In another bowl, whisk flour, baking powder, and salt.
Gradually mix dry ingredients into wet until just combined.
Fold in drained pineapple and shredded coconut.
In a small bowl, mix brown sugar with 1–2 tsp flour.
Roll dough into tablespoon-sized balls and coat in brown sugar mixture.
Place on baking sheets, flatten slightly, and add a maraschino cherry to each (if using).
Bake for 12–15 minutes, until edges are golden.
Cool on sheet for 5 minutes, then transfer to wire rack to cool completely.
