In a small saucepan, heat the berries, sugar and lemon juice over medium heat, stirring occasionally, until the berries have softened and the sugar has dissolved. Transfer the berry mixture to a fine mesh sieve set over a medium bowl. Using the back of a spoon or ladle, press on the berries to extract as much juice as possible. (You should have about 1/4 cup). Purée can be made, covered, and refrigerated one day in advance.

Line a 9 x 9-inch square pan with two (9 inch) sheets of parchment paper (overlapping perpendicularly), letting excess extend over sides of the pan; set aside.

In the bowl of a food processor, process the cookies, light brown sugar and butter until it resembles wet sand. Press the crumb mixture, evenly, onto the bottom of the prepared pan. Freeze until firm, at least 20 minutes.

In a medium bowl set over a pan of simmering water (making sure the bottom of the bowl doesn't touch the water), melt the chocolate and shortening, stirring occasionally, until smooth; set aside.

In a stand mixer fitted with the paddle attachment, beat the ream cheese, confectioners' sugar, vanilla, zest and salt at medium-low speed until smooth. Gradually beat in the melted chocolate. Transfer mixture to a large bowl; set aside.

Wipe the mixing bowl clean and return to the stand mixer fitted with the whisk attachment. Beat the cream and sugar at medium-high speed until stiff peaks form. Using a wire whisk or rubber spatula, fold in one-third of the whipped cream into the cream cheese mixture; fold in the remaining whipped cream until no streaks remain.

Pour half of the cream cheese mixture into the prepared pan, smoothing top with an off-set spatula. Spoon 2 tablespoons of purée mixture onto the filling and gently tilt the pan to evenly spread the purée. Dollop the remaining filling on top of the purée and gently spread in a even layer using an off-set spatula. Dollop remaining 2 tablespoons of purée on top of filling. Using a wooden picker edge of a clean knife, gently swirl purée and filling together. Freeze until firm, at least 4 hours or overnight. To serve, let sit at room temperature for 15 minutes. Using excess parchment as handles, remove from pan to a cutting board. Using a knife dipped in hot water and wiped dry each time you cut, cut into 16 bars.  Garnish with fresh blackberries and mint, if desired. Enjoy!