Line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal later.

In a large mixing bowl, whip the heavy cream until stiff peaks form.

In another bowl, combine the sweetened condensed milk and vanilla extract. Gently fold the whipped cream into the condensed milk mixture until well combined.

Place a layer of graham crackers at the bottom of the prepared baking dish, breaking them as needed to fit.

Spread half of the whipped cream mixture over the graham crackers, smoothing it out evenly.

Sprinkle half of the chopped strawberries and half of the blueberries over the whipped cream layer.

Add another layer of graham crackers on top, followed by the remaining whipped cream mixture.

Top with the remaining strawberries and blueberries, pressing them gently into the mixture.

Cover the dish with plastic wrap and freeze for at least 4 hours or until firm.

Once frozen, lift the treat out of the dish using the parchment overhang and cut into squares to serve.