Preheat your oven to 350°F (180°C). Lightly butter a 6-cup muffin tin or silicone mold to prevent sticking.
In a small saucepan over medium heat, combine the sugar and water. Let it cook without stirring until it turns a rich amber color. As soon as the caramel is ready, immediately pour it into the bottoms of the muffin cups, dividing it evenly.
Place half a pineapple slice in each muffin cup on top of the caramel. Gently press them down so they nestle in.
In a mixing bowl, whisk the eggs and sugar until pale and slightly thickened. Add the mascarpone and vanilla extract, mixing until smooth and creamy. Sift in the flour and baking powder, then gently fold until just combined.
Spoon the batter evenly over the pineapple slices in each cup, filling about ¾ of the way full. Bake for 20–25 minutes, or until a toothpick inserted into the center comes out clean and the tops are lightly golden.
Allow the cakes to cool in the tin for about 10 minutes. Then carefully flip them onto a serving plate while still warm so the caramel can gently coat the tops.
