Whip cream with powdered sugar and vanilla until soft peaks form.

Spread a thin layer of cream in an 8x8 pan.

Top with a single layer of graham crackers, breaking to fit.

Spoon on more cream, then scatter strawberries and blueberries.

Repeat layers until pan is full, finishing with cream and a few berries on top.

Cover tightly and chill at least 6 hours or overnight.

Slice with a sharp knife warmed under hot water for clean cuts.