Combine crust ingredients and press into bottom of 9 x 13-inch baking pan.
Cream together cream cheese, powdered sugar and milk until blended and smooth. Spread over crust carefully. Filling will be very thick.
Combine blackberry pie filling and vanilla extract. Gently smooth it over the top of the cream cheese layer.
Fold together whipped topping, sugar and vanilla. Gently spread over the blackberry pie filling. Cover tightly with plastic wrap; refrigerate for several hours or overnight. Keep refrigerated.