Slip a knife blade around the inside of the ring and lift off.
Transfer the tart to a serving plate and glaze the top with a little of the rhubarb syrup from stage 9.
Your apple and rhubarb tart is ready.
Remarks
If you prefer a thicker filling, make it with stewed apple instead of juice.
This tart looks nicer if there is a mixture of green and red rhubarb. This can be achieved by "cheating" slightly: At Stage 3, use a little grenadine syrup instead of sugar for half the rhubarb.