Preheat the oven to 120°C.
Lightly grease the base and sides of a 23cm springform tin and line the base with baking paper.
Place the digestive biscuits in a food processor and process into crumbs.
Tip into a bowl, pour in the melted butter and mix to combine.
Press into the tin, cover and refrigerate while making the filling. Place the cream cheese and sugar in a large bowl and beat until smooth (an electric mixer is good to use here), scraping down the sides occasionally.
Place the cream and chocolate in a microwave-proof bowl and microwave on high for 1 minute. Stir gently until smooth. Set aside. Mix lemon zest and juice into the cream cheese mixture.
Beat eggs in, one at a time. Lastly, fold through the cream and chocolate mixture. Remove the base from the refrigerator, pour in the filling and smooth the top. Place in the oven and bake for 1 hour or until the mixture has just about set (it will still be a little wobbly in the centre).
Cool the cheesecake before placing in the refrigerator until firm. Remove cheesecake from its tin and remove baking paper from the base. Place on a serving plate.
Decorate with whipped cream, fresh or freeze-dried blueberries and lemon zest.