Prepare the Pineapple Filling:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9×9-inch square baking dish or similar-sized baking pan.
2. Dice the Pineapple: If using fresh pineapple, peel and core the pineapple, then cut it into small, bite-sized pieces. If using canned pineapple, drain and pat dry the pieces.
3. Mix the Filling: In a bowl, combine the diced pineapple with the cornstarch (if using) and cinnamon. Toss to coat the pineapple evenly. Set aside.

Prepare the Batter:

4. Cream the Butter and Sugar: In a separate large bowl, beat the softened butter and sugar together with an electric mixer until light and fluffy.
5. Add the Eggs and Vanilla: Beat in the eggs, one at a time, ensuring each is fully incorporated before adding the next. Add the vanilla extract and beat again until smooth.
6. Combine Dry Ingredients: In another bowl, whisk together the flour, baking powder, and salt. Gradually add this mixture to the wet ingredients, stirring until just combined. The batter will be thick.
7. Add Pineapple: Gently fold the prepared pineapple mixture into the batter, ensuring an even distribution throughout.

Assemble the Bake:

8. Pour the Batter into the Pan: Transfer the batter into the prepared baking dish, spreading it out evenly with a spatula.
9. Bake the Sweet Bake: Bake in the preheated oven for 50-55 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
10. Cool and Serve: Remove from the oven and let the bake cool in the pan for about 10 minutes. Slice into squares and serve warm or at room temperature.