Preheat the oven to 220°C / 425°F / Gas Mark 7.
Place the pineapple slices, sugar and cinnamon into a small, ovenproof non-stick frying pan. Heat gently until the sugar has melted and the pineapple is caramelised.
Whisk the flour, eggs and milk together in a bowl. Stir in the sugar, vanilla essence and the mint leaves. You should have a thick mixture, the consistency of whipped cream. Add more milk if necessary.
Pour the mixture onto the pineapple and then transfer to the oven and bake for 15-20 minutes, until the sponge is golden and springy to the touch.
Remove from the oven and turn out onto a plate to serve warm. Cut into portions and serve with crème fraiche.