Line a muffin tin with paper cases, preheat the oven to 180 ° C and melt the butter over a double boiler or in the microwave. Drain the tangerines. Crumble the biscuits in the freezer bag with a rolling pin and mix with the butter and brown sugar. Pour the biscuit mixture into the muffin molds. Beat the sugar, egg and vanilla sugar with the mixer until frothy, add the cream cheese and sour cream and stir. Fold in the mandarins with a spoon, pour the filling over the biscuit mixture, bake for approx. 25 minutes and let cool down very well, as the tartlets are still very soft when they are warm.