Grease the base and side of an 18cm (base measurement) springform pan and line with baking paper.
Place biscuits in a food processor and process until finely crushed. Add butter and process until well combined. Spoon into the prepared pan and use a straight-sided glass to spread and press the biscuit mixture over base and side. Place in the fridge for 30 mins to chill.
Use an electric mixer to beat the cream cheese, sour cream and sugar in a bowl until smooth. Add the eggs and beat until well combined. Add the flour, lemon rind, lemon juice and vanilla and beat until well combined. Pour into the lined pan.
Place an upturned heatproof saucer or ramekin in the base of a slow cooker. Place the springform pan on saucer or ramekin. Cover and cook for 2 hours on high or until just set. Turn the slow cooker off. Leave the cheesecake in the slow cooker, partially covered, for 30 mins to cool. Place the cheesecake in the fridge for 3 hours to chill.
Meanwhile, to make the candied lemon, line a baking tray with baking paper. Combine the sugar and 1 cup (250ml) water in a small frying pan over medium-low heat. Cook for 3 mins or until the sugar dissolves. Add the lemon slices to the pan and cook, turning occasionally, for 30 mins or until the lemon rind is translucent. Transfer to the lined tray.
Transfer the cheesecake to a serving plate. Top with cream, candied lemon and lemon zest. Drizzle with the syrup from the candied lemon. Cut into wedges to serve.