MAKE THE CANDIED LEMON SLICES (OPTIONAL):

1. 1. Put the whole lemons in the freezer for 30 minutes. This will allow you to slice them extra-thin, a crucial move for this dish.

2. 2. Meanwhile, add 3 cups of the sugar to 4 cups of water in a small pot over high heat. Stir well so the sugar dissolves, and then allow the mixture to come to a boil.

3. 3. While the sugar water boils, use a serrated knife to slice the lemons width wise into the thinnest slices possible: 1/8 inch or less.

4. 4. Add the lemon slices to the pot and reduce the heat to keep the liquid at a low simmer. Cook the lemons until they are softened but not falling apart, about 15 minutes. This removes much of the bitterness from the lemons and begins the candying process.

5. 5. Remove the pot from the heat and allow the mixture to cool at room temperature for 15 minutes, so that it can be handled.

6. 6. Carefully strain the mixture, discarding the liquid and reserving the lemon slices.

7. 7. Add the remaining 4 cups of sugar to 4 cups of water in a small pot over high heat. Stir well so the sugar dissolves, and then allow the mixture to come to a boil.

8. 8. Add the lemon slices, reduce the heat to a low simmer, and continue cooking until the lemons are shiny and the syrup thickens, about 35 minutes.

9. 9. Remove the pot from heat and let the mixture cool completely at room temperature. Place the sliced lemons and the syrup in an air-tight container and refrigerate for at least 8 hours. The lemon slices will hold in the fridge for up to 1 week.

MAKE THE BISCOTA CRUST:

1. 1. Preheat the oven to 160°C

2. 2. In the food processor, grind the biscota into fine crumbs. (You should have about 2 cups.)

3. 3. In a medium mixing bowl, combine the biscotti crumbs, sugar and melted butter. Mix the ingredients together with your hands until everything is thoroughly incorporated and the mixture holds its shape when pressed together.

4. 4. Line a tart pan with the crust mixture, spreading it with your fingers and pressing down so that the mixture forms a thin layer around the entire pan.

5. 5. Bake the crust mixture until it turns golden brown and dry, about 10 minutes. Remove it from the oven and set it aside to cool at room temperature.

MAKE THE CHEESECAKE AND FINISH THE DISH:

1. 1. Return the oven to 160°C.

2. 2. Combine the ricotta cheese, sugar, eggs, heavy cream and lemon zest in a food processor with the blade attachment, and mix on medium until everything is thoroughly combined, about 2 minutes.

3. 3. Fill the crust completely with the cheesecake mixture. Return the tin to the oven and bake until a knife inserted in the cake comes out clean, about 20 to 25 minutes. Turn the cheesecake out onto a plate or a cookie rack and allow it to cool completely on the countertop. When the cheesecake is completely cool, refrigerate it for 2 hours. It will hold in the fridge up to 2 days.

4. 4. When you're ready to serve the cheesecake, remove the candied lemons from the fridge, if you're using them, and drain off any excess syrup. Garnish the top of the cheesecake with the candied slices, starting from the outside and working to the centre. You'll probably have extra lemons left over, so pick out the nicest slices to use. (If you're using a different topping, add it now.)

5. 5. Sprinkle the crushed pistachios over the top before serving.