1. Preheat the oven to 325°F (160°C) and prepare two racks—one at the bottom and one at the center.
2. For the crust, mix graham cracker crumbs (or crushed cookies), sugar, and melted butter. Press into a 9-inch springform pan or tart pan lined with baking paper. Bake for 8 minutes or refrigerate for 30 minutes for a no-bake version; cool completely.
3. Beat cream cheese and sugar until smooth. Add yogurt, flour, salt, and vanilla; mix well. Add eggs one at a time to blend gently.
4. Divide the batter: one portion plain, one with semi-sweet chocolate, one with dark chocolate and black cocoa (for darkest).
5. Layer batters in crust: plain, semi-sweet chocolate, then dark chocolate, smoothing each. Ensure distinct layers for ombré effect.
6. For water bath baking, place a pan with boiling water on the bottom rack. Center the springform pan above.
7. Bake 65-70 minutes until edges set, center jiggles. Cool in oven, door cracked, 1 hour. Knife around edges after 30 minutes.
8. Cool to room temperature, then chill 4-6 hours or overnight until set.
9. For ganache, heat cream to steaming, remove from heat, whisk in chocolate until smooth. Cool, then pour over chilled cheesecake. Decorate with shavings.
10. Chill briefly before serving cold.