Prepare the Pan u0026 Oven : Preheat to 325°F (160°C). Line bottom of a 9-inch springform pan with parchment.
Make the Carrot Cake Batter : Whisk flour, cinnamon, nutmeg, baking soda, and salt. In a separate bowl, mix both sugars + oil + eggs + vanilla. Combine wet and dry mixtures gently. Fold in grated carrots and nuts if using. Pour batter into prepared pan and spread evenly.
Make Cheesecake Filling : Beat cream cheese until smooth. Add sugar, mixing until creamy. Add eggs one at a time (low speed). Mix in sour cream and vanilla.
Assemble : Carefully pour cheesecake filling over carrot cake batter.
Bake : Bake 60–75 minutes until set with a slight jiggle in the center. Optional: water bath for extra smoothness (pan wrapped in foil). Turn off oven, crack door open 1 hour to cool gradually.
Chill : Refrigerate at least 6 hours or overnight.
Frost : Beat frosting ingredients until fluffy. Spread over chilled cheesecake. Add decorative nuts or carrot curls if desired.