In a small bowl, combine sugar and cornstarch and mix well. In a medium saucepan, heat water and thawed raspberries and juices to boil. Reduce heat to low and add cornstarch mixture, whisking until well combined. Simmer, whisking until mixture is thickened and just coats the back of a spoon. Remove from heat and cool to room temperature.
In a large bowl, combine tahini and milk and blend until smooth. Stir in honey until smooth.
In a large bowl, with an electric mixer, beat cream until soft peaks form. Fold 1 cup (250 mL) of whipped cream into tahini mixture to lighten. Slowly fold in remaining cream until combined.
In a medium bowl, combine espresso and Grand Marnier, if using.
Dip each lady finger in espresso mixture to coat both sides. Do not allow the cookies to become soaked. Place one-quarter of the cookies in a single layer on the bottom of a trifle bowl, cutting to fit if necessary. Spoon one-quarter of the raspberry sauce over lady fingers and then layer in one-quarter of the tahini cream. Dust lightly with cocoa powder. Repeat three more times finishing with tahini cream.
Refrigerate for 2 hours or more. When ready to serve, arrange fresh raspberries on top of trifle and lightly dust with cocoa if desired. Garnish with fresh mint leaves, if using and serve!