To make the anglaise base for the mousse, bring the milk and cream to a boil over medium heat. Whisk together the egg yolks and the sugar and temper them with the hot mixture. Cook to nappé. Strain.
Bloom the gelatin sheets in cold water, then squeeze out excess water. Scale out 5¼ oz/150 g of the warm anglaise and add the gelatin, stirring to dissolve.