This lemon cheesecake is perfect for those who like a "sour face". If you are not a huge fan, omit the lemon curd or increase the amount of sugar used in the curd.
Preheat the oven to 180 degrees Celsius (355 degrees Fahrenheit). Line a baking sheet with aluminum foil or baking paper and place 4 cake rings on top (my cake rings are 2 1/2-inch in diameter and 1 3/4-inch tall). Set aside.
Process or crush the biscuits into fine crumbs. Add in butter and mix until you get a damp sand consistency. Divide the mixture among the 4 cake rings and press down firmly with the back of a spoon. Use a toothpick or a fork, poke holes on the crust so that the crust will not separate from the cheesecake.
Using a wooden spoon or an electric mixer, beat cream cheese, sugar, egg and lemon juice together until combined (use a low speed if using an electric mixer). The key is to incorporate as little air as possible into the cheesecakes. Divide the batter among the cake rings and bake for 20 to 25 minutes until the cheesecake is set but there is still a very slight wobble in the middle. Place the baking sheet on a wire rack and set aside to cool while you make the lemon curd.
Lemon Curd
Combine the lemon zest, lemon juice and sugar in a small pot and bring to a simmer. Whisk the egg yolks in a separate mixing bowl.
While whisking the egg yolks, slowly drizzle in the hot lemon syrup, drop by drop, then in a tiny stream until all the lemon syrup has been added. This process is called tempering.
Return the mixture into the pot and cook over medium-low heat. Stir constantly until the mixture has thickened. A sure sign is that when you scrape the bottom of the pot, the curd does not fill the void immediately and that the consistency is thick enough to coat the back of a spoon. Place the pot in a large bowl of ice water to stop the cooking.
Assembly
Divide the lemon curd among the cheesecakes the refrigerate the cheesecakes for at least 4 hours or overnight.
To serve, wrap the cake rings with a warm tea towel for a few minutes then push the cheesecakes out from the bottom gently and slowly. Place on a serving plate and serve.