Cut the apricots into fine cubes and boil them with 2 tbsp. water, 2 tbsp. apricot liqueur and juice of one lemon in a saucepan while stirring and steam them over medium heat for 2-3 min until the liquid has evaporated completely. Cool, fill into 4 glasses (a 250 ml capacity) and set aside to cool.
Soak the gelatine in cold water. Make 150 ml of cremant with the remaining apricot liqueur and 100 g of sugar over medium heat until the sugar has dissolved, stirring constantly. Remove the cremant mixture from the heat and let the squeezed gelatin melt in it.
Put the liquid in a baking dish to cool. As soon as it starts to gelatinize, fold in the remaining cremant. Keep the resulting foam going back a little at a time, then pour in another little bit of cremant. Pour the mixture into the glasses and refrigerate for at least 2-3 hours.
Rinse and clean the rhubarb and cut it into fine slices. Bring to a boil in a saucepan with 50 ml of water and the remaining sugar. Do this, stirring, until the rhubarb is completely broken down and the liquid has evaporated completely. Cool the rhubarb compote and set aside to cool. Just before serving, spread evenly over the jelly.