Make 2 small slits on opposite sides of 4 small plastic cups. Fill them with some melted dark chocolate and swirl around to coat the cups. Remove the melted dark chocolate back into the chocolate bowl. Refrigerate the chocolate cups till set. Similarly coat the tart shells with remaining melted dark chocolate and refrigerate till set.
To prepare phirni, heat milk in a non-stick pan.
Grind the drained India Gate Basmati Rice alongwith 1-2 tbsps milk to make a fine paste. Add the ground paste to hot milk, mix and cook on low heat till it thickens.
Add castor sugar, mix and cook till it melts. Switch off heat, add cocoa powder and khoya and mix well till khoya melts. Stir the mixture continuously and bring down to room temperature.
Fill the phirni in a piping bag and refrigerate to chill.
Demould the chocolate cups from the plastic cups and tart shells.
Place chocolate tarts and cups on an individual platter and pipe out phirni in each. Serve immediately garnished with mint leaves.