Butter a 28 x 28 cm tray or any oven dish that is around 28 cm and scatter the remaining butter in little knobs on the bottom of the tray.
Cut the pineapple into 1cm (½ inch) thick rings, remove the hard middle part and arrange it on the bottom of the tray/dish. Cut a ring or two into smaller pieces to cover the bigger gaps. Put the berries in the centre of the pineapples rings and into the small gaps.
Sprinkle half of the Demerara/ Muscovado sugar over the pineapple and put it in the oven for 20 mins. After 20 mins, take it out and allow it to cool slightly.
Meanwhile in a bowl, beat the eggs with a pinch of salt, sugar and gradually, while still mixing, add the oil. Beat until is all nice and fluffy. You can beat yolks and whites separately however this isn't necessary.
In a separate bowl mix the flour, baking powder and the soda bicarbonate which needs mixing with the spoon of cider vinegar and added to the flour.
Add the egg mixture and the yoghurt to the flour and mix well with a spatula until it is well homogenized.
Pour this mixture over the cooled pineapple, sprinkle the remainder of the Demerara sugar and place in the oven.
Bake for about 25 minutes at 180C/350F and then increase to 190C/380F and bake for another 20-25 min until is nice and golden. Turn the oven off but do not take the cake out. Instead, open slightly the oven (about 2-3 cm, maybe place a towel to help keep the oven door ajar) and wait until it is almost cool.
Notes
Resting time is optional as it might be tough to smell this and not have a tuck-in ;-). The yoghurt should definitely be half or full fat, no point cutting calories here, it is a dessert after all.Enjoy it, it is a really delicious cake, light and it has different textures which I absolutely love. Custardy in places, airy in some and then you get the fruit texture and flavours. Delish! Mmmmm