1. Preheat oven to 325°F. Wrap a 9" springform pan in foil.
2. Mix crushed Oreos, butter, and salt. Press into pan base and halfway up the sides. Bake 10 minutes.
3. In a large bowl, beat cream cheese until smooth. Add sugar and espresso powder; beat until fully combined.
4. Add sour cream, vanilla, and liqueur (if using). Mix well.
5. Add eggs one at a time, beating gently to avoid overmixing.
6. Pour filling into crust. Tap pan to release air bubbles.
7. Place pan in a larger roasting dish. Pour hot water halfway up the sides (water bath).
8. Bake 55–65 minutes, until center is slightly jiggly.
9. Turn off oven, crack the door, and let cool inside for 1 hour.
10. Refrigerate at least 4 hours or overnight. Top and serve chilled.