Make the Sugar Cookie Crust:

• Preheat and Prep: Preheat oven to 350°F (175°C). Spray a 9-inch springform pan with baking spray (one with flour and oil). Line the bottom of the pan with a 9-inch circle of parchment paper. Spray the parchment paper and the sides of the pan again. Set aside.
• Combine Dry Ingredients: In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
• Cream Butter and Sugar: In a large bowl, using an electric mixer (stand mixer or hand mixer), beat the softened butter and sugar together on high speed for 2 minutes, until light and fluffy.
• Add Wet Ingredients: Add the vanilla extract, egg, and egg yolk. Beat on medium speed until well combined.
• Combine Wet and Dry: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix.
• Add Sprinkles: Stir in the Christmas sprinkles.
• Press into Pan: Pour the cookie dough into the prepared springform pan. Use your hands or an offset spatula to press the dough evenly across the bottom of the pan. It does not need to go up the sides.
• Bake: Bake for 25-30 minutes, or until the crust is golden brown.
• Cool: Let the crust cool completely in the pan while you prepare the cookie dough balls and cheesecake filling.

2. Make the Cookie Dough Balls:

• Combine Dry Ingredients: In a medium bowl, whisk together the flour and salt. Set aside.
• Cream Butter and Sugar: In a separate large bowl, using an electric mixer, beat the softened butter and sugar together on high speed for 2 minutes, until light and fluffy.
• Add Wet Ingredients: Beat in the vanilla extract and milk until well combined.
• Combine Wet and Dry: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined.
• Add Sprinkles: Stir in the Christmas sprinkles.
• Roll into Balls: Line a baking sheet with wax paper or parchment paper. Using your hands, roll the cookie dough into small balls, about the size of a dime or nickel (about 1/2 teaspoon each).
• Freeze: Place the cookie dough balls on the prepared baking sheet and freeze until solid. This will prevent them from spreading too much in the cheesecake.

3. Make the Cheesecake Filling:

• Preheat Oven: Reduce the oven temperature to 325°F (163°C).
• Prepare Water Bath Water: Bring a pot of water to a boil (this will be for the water bath).
• Beat Cream Cheese and Sugar: In a large bowl (or the bowl of a stand mixer), beat the softened cream cheese and sugar together on high speed for 2 minutes, until completely smooth and creamy. Scrape down the sides of the bowl halfway through.
• Add Sour Cream, Heavy Cream, and Vanilla: Add the sour cream, heavy cream, and vanilla extract. Beat on medium speed until smooth and well combined. Make sure there are no lumps of cream cheese.
• Add Eggs: Add the eggs one at a time, mixing on low speed until just combined after each addition. Do not overmix.
• Fold in Cookie Dough: Remove the bowl from the mixer. Gently fold in 2/3 of the frozen cookie dough balls.

4. Assemble and Bake the Cheesecake:

• Pour Filling: Pour the cheesecake batter over the cooled sugar cookie crust in the springform pan.
• Prepare Water Bath: Wrap the outside of the springform pan tightly with several layers of heavy-duty aluminum foil to prevent water from seeping in. Place the wrapped springform pan inside a larger roasting pan.
• Add Water: Carefully pour the hot water into the roasting pan, filling it about halfway up the sides of the springform pan. The water should not come above the top edge of the aluminum foil.
• Bake: Bake for 80-90 minutes, or until the edges of the cheesecake are set and the center has a slight jiggle.
• Cool in Oven: Turn off the oven, but leave the cheesecake inside with the oven door closed for 30 minutes. Then, crack open the oven door and let the cheesecake cool slowly for another 30 minutes. This gradual cooling helps prevent cracks.
• Cool and Chill: Remove the cheesecake from the oven and water bath. Carefully remove the aluminum foil. Let the cheesecake cool completely to room temperature on a wire rack. Then, cover the pan tightly with plastic wrap and refrigerate for at least 6 hours, or preferably overnight.

5. Make the White Chocolate Ganache:

• Chop Chocolate (if needed): If using white chocolate bars, chop them into small, even pieces. Place the white chocolate chips (or chopped white chocolate) in a heatproof bowl.
• Heat Cream: In a small saucepan, heat the heavy cream over medium heat until it is hot and steaming, but not boiling.
• Pour Cream over Chocolate: Pour the hot cream over the white chocolate.
• Let Sit: Let the mixture sit undisturbed for 2 minutes.
• Stir: Stir gently with a rubber spatula or whisk until the chocolate is completely melted and the ganache is smooth. If any unmelted chocolate remains, microwave in 20-second intervals, stirring after each interval, until smooth.

6. Finish and Serve:

• Remove Cheesecake from Pan: Once the cheesecake is completely chilled, carefully remove the sides of the springform pan. Remove the parchment paper from the bottom.
• Pour Ganache: Pour the white chocolate ganache evenly over the top of the cheesecake.
• Freeze Briefly: Place the cheesecake in the freezer for about 10 minutes to set the ganache slightly.
• Add Toppings: Top with the remaining frozen cookie dough balls and additional Christmas sprinkles, if desired.
• Slice and Serve: Slice the cheesecake with a sharp, clean knife, wiping the blade clean between each cut.