1. Prepare the Crust:

1. In a medium saucepan, combine blackberries, water, and 1/4 cup sugar. Cook over medium heat until blackberries break down and mixture thickens, about 10 minutes. Strain through a fine-mesh sieve and let cool.
2. In a large bowl, whip heavy cream and remaining 1/4 cup sugar until soft peaks form. Fold in lemon juice, lemon zest, and cooled blackberry puree until just combined.
3. Pour the mixture into silicone sphere molds (about 2 inches in diameter). Freeze for at least 6 hours or until solid.
4. In a heatproof bowl, melt dark chocolate and coconut oil together over a double boiler until smooth. Let cool slightly.
5. Remove frozen spheres from molds and place on a parchment-lined baking sheet. Working quickly, pour or dip each sphere into melted chocolate to coat completely. Return to baking sheet.
6. Freeze for another 30 minutes to set the chocolate shell. Serve immediately or store in the freezer for up to 1 week.