Strawberry Cotton Soft Japanese Cheesecakes

(adapted from this recipe, makes about 14 cupcake sized cheesecakes)
140g/5 oz. fine granulated sugar
6 egg whites
6 egg yolks
1/4 tsp. cream of tartar
50g/2 oz. butter
250g/9 oz. cream cheese
100 ml/3 fluid oz. fresh milk
1 tbsp. lemon juice
60g/2 oz. cake flour /superfine flour
20g/1 oz. cornflour (cornstarch)
250g strawberry jam
Optional: White chocolate buttons

Melt cream cheese, butter and milk over a double boiler. I used a whisk to break up any lumps. Cool the mixture. Fold in the flour, the cornflour, egg yolks, lemon juice and mix well.
Whisk egg whites with cream of tartar until foamy. Add in the sugar and whisk until soft peaks form.
Add the cheese mixture to the egg white mixture and gently fold until just combined. Spoon into cupcake tray lined with paper liners, filling to about 5/6ths full.
Bake cheesecake in a water bath (I placed my cupcake tray in a roasting tray that was 3/4 filled with water) for approximately 30 mins or until set and golden brown at 160 degrees C (325 degrees F). A skewer inserted into the centre should come out with some moist crumbs attached. To avoid the cheesecakes cracking or collapsing, turn the oven off right before they are ready and then leave the oven door slightly open so they cool gradually. After 5 minutes, remove them from the oven and let them sit in the tray for another 10 minutes. Remove from the tray and leave to cool completely on a wire rack.
While the cheesecakes are baking, place strawberry jam in a small saucepan and gently heat, stirring until smooth. Set aside to cool and set slightly. When your cheesecakes have cooled, spoon a layer of strawberry jam over the top.
Optional: Decorate with white chocolate buttons to make them look like toadstools, which is kind of awesome. Leave to set for about half an hour and then remove paper cases before serving. Can be stored in fridge overnight.