When the cake is done, invert immediately and cool upside down in the pan, to prevent it from sinking. Use the feet of the pan to hold it above the surface of the table or prop it higher by resting the tube on a bottle or inverted funnel. Let the cake cool for at least 1 1/2 hours, until it is thoroughly set. Remove it from the pan before storing: slide a thin knife around the cake to detach it from the pan. Using the same procedure, detach the cake from the tube.