In a medium saucepan over medium heat, combine fresh blackberries, optional Grand Marnier, fresh lemon juice, and sugar. Cook until it begins to boil, stirring occasionally for about 2-3 minutes. Once boiling, reduce heat and let simmer for 8-10 minutes until thickened. Remove from heat and cool completely.

In a small bowl, sprinkle unflavored gelatin over cold water and let sit for about 5 minutes to bloom. Heat in microwave for 10-15 seconds until dissolved.

In a large mixing bowl, use an electric mixer to whip heavy cream on medium speed until it thickens. Gradually add powdered sugar and vanilla, whipping until soft peaks form.

Gently pour the dissolved gelatin mixture into the whipped cream while mixing on low speed until combined.

Incorporate the plain Greek yogurt into the whipped cream mixture, gently folding until fully combined.

In clear glasses, layer the cooled blackberry syrup and creamy yogurt mixture. Start with syrup, followed by cream, and repeat.

Top with fresh blackberries and a mint leaf. Cover and refrigerate for at least 2 hours.