Preheat the oven to 180c (300F)
Butter a 24cm springform cake tin and line the bottom with baking paper. This is the perfect size to fit the pineapple rings in neatly. If you don't have as big a tin, you can cut the pineapple rings in half, and arrange them fanning out from the centre.
Mix the brown sugar and and 50g of butter in a small saucepan and melt. Combine well.
Spoon or pour the caramel into the base of the pan.
Arrange the pineapple slices over the caramel mixture and put it to one side.
Meanwhile, using an electric whisk, beat the remaining butter with the sugar until smooth, then beat in the eggs one at a time. You want to do this to avoid the eggs and batter curdling.
Fold in the flour, baking powder, and salt into the batter, then add the vanilla essence and milk and combine.
Spoon the batter over the pineapple rings and smooth down with a palette knife.
Bake the cake for around 35-40 minutes until it is golden in color and a skewer inserted into the middle of the cake comes out clean.
Let the cake cool in the cake tin for 10 minutes.
Remove the sides of the springform cake time and carefully turn the cake onto a plate so the pineapple is now on top. You may need to gently peel off the baking paper.
Serve large slices of the cake, alongside some whipped cream or vanilla ice cream.