Hello, NC. I made the lemon “cream” illusion about a year ago, and loved it. I did use the gelatin, but still it seemed pretty soft. I used it as a cake filling between layers of classic genoise, and used a buttercream dam around the edge to be sure there wouldn’t be any problems. It sliced well (no dripping or running) and had the most ethereal texture- disappeared in your mouth, yet left an intense lemon flavor. I used lemon curd mousseline as the outside frosting- truly a labor of love!
I don’t think it’s firm enough to frost a cake, it’s meant to be a filling. However, it does firm up some as the gelatin sets. I can think of two simple presentations for it. One is to roll it with vanilla or almond or ginger Biscuit Roulade (definitely doesn’t need the optional syrup) and top with powdered sugar at serving time (similar presentation to almond biscuit roulade with raspberry cloud cream on p12 of TCB). The other would be to layer it between torted layers of yellow cake, leaving the sides unfrosted so that the filling is visible peeking out between layers, and putting a thicker, more swriled mound on top of the cake. With either presentation you could add fresh raspberries for garnish.
Whatever you do, make sure the cake is thoroughly chilled to set the gelatin (if stacking layers you can chill them first), then you can bring it to room temp. at serving time.
Oh, there you’ve done it, now I want to eat some lemon cake!
Good Luck and let us know what you go with.