Step 1

Stir together crushed vanilla wafers and melted butter in a medium bowl until combined. Firmly press into bottom and about 1/2 inch up sides of a 9-inch springform pan. Freeze, uncovered, while you prepare filling.

Step 2

Beat cream cheese and 1/2 cup of the powdered sugar with a stand mixer fitted with a paddle attachment on medium-low speed until smooth, about 2 minutes. Add mascarpone, and beat until just combined, about 30 seconds. Transfer mascarpone mixture to a large bowl. (Do not wipe mixing bowl clean.)

Step 3

Add heavy cream, vanilla, and remaining 1/4 cup powdered sugar to bowl, and beat with stand mixer fitted with a whisk attachment on high speed until stiff peaks form, about 2 minutes. Add whipped cream to mascarpone mixture in 3 separate additions, gently folding until just combined after each addition. Remove springform pan from freezer, and spoon mascarpone mixture over crust, smoothing top with a spatula. Freeze, uncovered, until firm, about 3 hours.

Step 4

Gently stir together raspberry jam, raspberries, and blueberries in a small bowl. Spoon evenly over cheesecake. Freeze, uncovered, until firm, about 1 hour. Remove sides of pan, and serve immediately. Store loosely covered in refrigerator for up to 3 days.