Preheat the oven to 170c/fan 150c and grease and base-line a 23 cm springform tin with baking paper. Crush the digestive biscuits to fine crumbs using either a rolling pin or a food processor. Melt 60 g of the butter in a small saucepan, add to the biscuits and stir together until combined. Spoon into the prepared tin and press the mixture down firmly. Chill for at least 15 minutes.

Place the remaining butter, caster sugar and the vanilla essence in a bowl and using electric beaters, beat until light and fluffy. Beat in the egg yolks and the lemon juice. Then add the cream and mascarpone and continue beating until smooth.

In a clean bowl, whisk the egg whites until just stiff. Add about a third of the egg whites to the cheesecake along with the blueberries. Pour onto the biscuit base and level the surface. Place the tin on a baking tray and bake for 1 hour until the top is lightly golden and just set (it should have a slight wobble to it).

When cooked, turn off the oven and leave the cheesecake inside to cool, leaving the door ajar. Expect some fat to collect in the tray.Carefully remove the cheesecake from the tin and serve dusted with sifted icing sugar.