Mash the bananas or purée with an electric hand mixer. Mix with the milk, sugar and almond and vanilla essence.
Put 2 tablespoons of cold water in a small bowl and sprinkle the gelatine over the top. Leave to sponge for 5 minutes without stirring.
Heat the banana mixture in a saucepan almost to boiling, whisking or stirring constantly, then remove from the heat. Stir the gelatine into the mixture and keep stirring until completely dissolved. Pour into a large (at least 800 ml capacity) decorative jelly mould and chill until set.
Once gelatine is added to liquid, the liquid should not be boiled or the gelatine may not set properly.