Step 1: Prepare the Cheesecake Filling

1. In a small bowl, mix the cream cheese and sugar until smooth.
2. Stir in the vanilla extract and sour cream, mixing until creamy.
3. Scoop out 2-teaspoon-sized dollops onto a parchment-lined baking sheet and freeze for 30 minutes, or until firm.

Step 2: Make the Cookie Dough

4. In a large bowl, cream together the butter, granulated sugar, and brown sugar until light and fluffy.
5. Mix in the egg and vanilla extract until well combined.
6. In a separate bowl, whisk together the flour, graham cracker crumbs, cornstarch, baking soda, and salt.
7. Gradually add the dry ingredients into the wet ingredients, mixing until just combined.
8. Cover the dough and refrigerate for 30 minutes.

Step 3: Assemble the Cookies

9. Roll 2 tablespoons of dough into a ball and press a deep indentation in the center.
10. Fill the indentation with 1 ½ teaspoons of strawberry jam.
11. Place a frozen cheesecake dollop on top of the jam.
12. Roll another small piece of dough, flatten it, and seal it over the filling, ensuring no gaps.

Step 4: Bake the Cookies

13. Preheat oven to 375°F (190°C).
14. If using, press chopped white chocolate onto the tops of the cookies.
15. Place cookies on a parchment-lined baking sheet and bake for 14-15 minutes, or until golden brown.
16. Let cookies cool on the baking sheet before transferring—warm cookies will be fragile.