Preheat oven to 350°F (175°C) and grease a 9-inch round cake pan.
In a large mixing bowl, whisk together the sweetened condensed milk, eggs, melted butter, and vanilla until smooth.
In a separate bowl, combine flour, baking powder, and salt. Gradually add to the wet ingredients, stirring until just combined.
Fold in the crushed pineapple gently.
Pour the batter into the prepared pan and smooth the top.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Cool in the pan for 10 minutes before transferring to a wire rack. Serve warm or chilled.