Wash and trim rhubarb. If the stalks are thick, remove the outer layer. Cut into 1 to 2cm pieces. Add to a saucepan with the sugar and butter and bring to the boil. Reduce the heat and simmer until the rhubarb is soft. Drain the rhubarb and reserve the liquid. Let cool.
In a bowl add quark and cream cheese and stir till smooth. Add orange extract and sugar and stir to combine. Whip the cream and fold it in.
Dip half of the sponge biscuits into the reserved rhubarb liquid and place in a rectangular dish. Top with half the quark mixture and spread evenly, then add half of the drained rhubarb. Repeat this but don't dip the second layer of the sponge biscuits, just place them with their sugary side down on the rhubarb so they can soak up the liquid. Finally, end with a quark layer.
Cover with cling film and refrigerate overnight. Just before serving, slice the strawberries and spread over the top like a fan for garnish.