I second a recommendation for aquafaba chocolate mousse. I make it regularly, and it's so simple and effective.
My recipe is just aquafaba (chickpea water) from one tin of chickpeas (I usually use Suma organic); 100g of dark chocolate (I use 70% Green & Blacks); a few drops of vanilla extract, and about 3 dessert spoons of icing sugar (or more or less to taste)
Whisk the aquafaba for a few minutes to stiff peaks and melt chocolate in a bowl over a pan of boiling water. I usually multitask with these - keep an eye on the melting chocolate, while whisking the fluff! I let the chocolate cool a little while adding the sieved icing sugar and vanilla to the fluff, gradually while whisking.
You need to gently fold the fluff into the chocolate. But to prevent separation, first take about a quarter of it (the fluff) and mix quickly with the chocolate to kind of render it more receptive of the remaining fluff. Gently fold in the remaining fluff with a spatula until all combined. Spoon into little serving bowls or ramekins of choice. Refrigerate till set.
It's light and fluffy and yummy! Sometimes some of the chocolate hardens into little tiny chips in the mousse. I pretend it's deliberate, and call it chocolate chip mousse! 😉
Enjoy!