1) Bloom gelatin sheets in cold water. Combine liqueur and vanilla seeds in a small saucepan over low heat.
2) Once gelatine sheets have bloomed, add to the saucepan to dissolve.
3) Whip double cream and icing sugar to soft peaks. Once the gelatine has dissolved, pour into the whipped cream and begin whisking on high speed to combine. Pour into glasses and allow to set up overnight.