I confess I never heard of a entremet cake. Had to google it. You don’t have to make a mousse cake to get the effects. What I believe your looking for is a mirror glaze cake. Just google mirror glaze and many tutorials will pop up. But if mouse cake is what you’re seeking, Google just that.
Hope this helps.
Creativity is God's gift to us. Using our creativity is our gift back to God. Clarky's Cakes 😎