Crush Oreo cookies into fine crumbs and mix with melted vegan butter until resembling wet sand. Press into a 9-inch tart pan and freeze for 15 minutes.

Blend blackberries and blueberries until smooth. Strain if desired to remove seeds.

In a bowl, mix berry puree with non-dairy cream cheese, sugar, and vanilla until creamy.

Whip non-dairy cream until stiff peaks form, then fold into berry mixture gently.

Dissolve agar powder in non-dairy milk, heat until gentle boil, then let cool slightly.

Fold cooled agar into the berry filling, pour into crust, and refrigerate for at least 4 hours.

Garnish with fresh berries before serving. Cut into slices and serve chilled.