Run very hot water in your kitchen sink and place the bottom of the terrine dish in the water, in order to detach the gelatine from the mould. Take a knife with a very thin blade and gently run the blade between the glass and the terrine, all the way around. Place a wooden board over the terrine dish, flip it over, and the terrine should come loose. Some people prefer to line the terrine dish with clingwrap before putting in the first layer, then when it is time to remove the mould you simply pull the clingwrap at each side when you’ve turned the terrine upside-down on a board. But it can be difficult to get the wrap smooth enough. If you use clingwrap, it helps a great deal to paint the inside of the dish with melted butter first, then push the wrap into the corners so that the terrine is square, not rounded. It’s up to you.