01 - Preheat oven to 340°F. Line a 9-inch springform pan with parchment paper on the base and lightly grease the sides.
02 - Combine crushed graham crackers, sugar, and melted butter in a bowl until evenly moistened. Press the mixture firmly into the bottom of the prepared pan. Bake for 10 minutes, then set aside to cool.
03 - Using an electric mixer, beat softened cream cheese and sugar together until smooth and creamy. Add eggs one at a time, beating well after each addition. Blend in mashed bananas, vanilla extract, sour cream, and cornstarch until the batter is fully combined and uniform.
04 - Pour the filling over the cooled crust and smooth the surface with a spatula. Bake for 50 to 60 minutes, until the center is just set but still slightly wobbly when gently shaken.
05 - Allow the cheesecake to cool at room temperature for 1 hour, then transfer to the refrigerator and chill for at least 3 hours, preferably overnight for best results.
06 - Toss sliced strawberries with strawberry jam and lemon juice until evenly coated. Arrange the strawberry mixture over the chilled cheesecake. Garnish with additional fresh banana and strawberry slices if desired. Slice and serve chilled.