Line a round 8 or 9 inch round pan with plastic wrap , such that wrap is above the sides of the pan. You could alternately use a springform pan or mousse ring for smoother sides.
To make the base, melt the butter and add crushed biscuits. Mix well and press into the base of pan.
Chill for atleast 30 minutes or until your mousse is ready.
Sprinkle the gelatin over the cold water in a small bowl. Keep aside.
Blend together the seeds (Arils ) of the pomegranate in your mixer or food processor.
Strain into a sauce pan ( to get rid of the graininess) and add the sugar. Heat on low until it starts to bubble .
Take off the heat and add the lemon juice and gelatin mixture. Mix until all gelatin granules are dissolved. You could strain it again if you wish. Let this come to room temperature. Whisk in between if you feel its forming a jelly.
Whip up the cream to soft peaks.
Fold the cream into the pomegranate mixture until smooth.
Pour onto your chilled base and smoothen the top. Chill for 6 hours or overnight. When you are ready to serve, just lift the plastic wrap out (or unmold if using a mousse ring/ springiform pan) and transfer the tart to the serving dish.