Preheat oven to 325°F (163°C). In a bowl, combine graham cracker crumbs, 0.25 cups sugar, and melted butter. Press into the bottom of a 9-inch springform pan.
In a large mixing bowl, beat softened cream cheese until smooth. Add 1 cup sugar and vanilla extract; mix well.
Add eggs one at a time, mixing on low speed after each addition. Stir in sour cream until just combined.
In a blender or food processor, puree fresh raspberries with 0.25 cups sugar until smooth. Strain to remove seeds if desired.
Pour half of the cheesecake batter into the prepared crust. Drop spoonfuls of raspberry puree over the batter, then add the remaining cheesecake batter on top.
Using a knife or skewer, gently swirl the raspberry puree through the cheesecake batter to create a marbled effect.
Bake for 55-60 minutes or until the center is almost set but still slightly jiggly. Turn off oven and leave cheesecake in oven with door slightly open for 1 hour.
Remove from oven and cool to room temperature. Refrigerate for at least 4 hours or overnight before serving.
Notes
For best results, use fresh ripe raspberries and make sure the cream cheese is fully softened before mixing to avoid lumps.