1. Preheat oven 350°F/176°C. *See note below if you plan to bake one whole cheesecake in a springform pan. 
2. Prepare the Biscoff cookie crust. Add the cookies to the bowl of a food processor. Pulse to crush the cookies until they resemble coarse sand. If using a plastic freezer bag and a rolling pin to crush the cookies, place the cookies into the bag, seal, and pound the cookies to crush them. Add the melted butter and combine well. Evenly distribute the cookie mixture to the ramekins (or prepared springform pan or pie plate) and press it down using the back of your hand or a jar to form a compact crust. Bake for 7 minutes, or until set. Remove from oven and place the ramekins into an oven-safe dish with deeper sides so that the mini cheesecakes can be baked in a water bath.
3. Melt the white chocolate. Place a medium bowl over a smaller pot with water to create a double boiler making sure the sides of the bowl are wider than the pot. Melt the chocolate slowly and turn off the heat. Alternatively, you may microwave the white chocolate for a few seconds, being sure to turn it off every 5 seconds or so and stirring it. Remove as soon as it's melted.
4. Prepare the cheesecake base. Using a handheld mixer (or stand mixer fitted with the paddle attachment), cream the sugar, cream cheese, and mascarpone until light and fluffy about 2 minutes. Add eggs, vanilla, sour cream, and salt and mix just until combined and no traces of egg are left. Add the heavy cream and lemon juice and stir to combine using a spatula. Next, add the melted white chocolate and stir to combine. Lastly, stir in the flour until no traces of flour remain. Do not over-mix once you add the flour. 
5. Fill the ramekins (or springform cake pan). Evenly distribute the cheesecake batter amongst the ramekins (or pour directly into the springform cake pan if using). Give them a gentle but firm "tap-tap" to remove any air bubbles.
6. Prepare the water bath. Heat about 1 quart/liter of water in a pot until almost boiling. Pour it into a liquid measuring cup or a pitcher with a pour spout. This will make it easier to get the hot water into the baking vessel to form the hot water bath without spilling all over the oven.
7. Bake the cheesecake.  Working quickly add the pan containing the filled ramekins (or springform pan) to the oven. Gently and slowly, pour the hot water into the hot water bath vessel being sure not to splash water into the cheesecake. Close the oven door and bake for approximately 25 minutes, or until the top is puffy and set, but not browned. The middle should slightly bounce or jiggle and you should be able to lightly touch the tops without it sticking to your finger when the cheesecake is ready. Remove it from the oven to a wire rack and allow to cool completely. Wrap and refrigerate for at least 5 hours and even better overnight. Serve with your favorite homemade fruit sauce like strawberry coulis or fruitti di bosco coulis Enjoy!

*If baking one whole cheesecake in a springform pan, prepare it by buttering an 8, 9, or 10-inch springform pan and lining it with parchment paper on the bottom and sides. Proceed with the remaining instructions, and be sure to wrap the pan well with heavy-duty aluminum foil in preparation for the hot water bath.  You'll also need to adjust baking times. Reference specifics in the recipe notes.