Step 1Place the raspberries and sugar in a heatproof bowl. Cover tightly with plastic wrap and place on top of a pan of simmering water. Let the heat release the juices from the berries; this will take about 30 minutes. When you’ve got a nice pool of juice, pour the lot into a sieve lined with a clean tea towel over a measuring cup or another bowl, and set aside until the clear juice finishes dripping through.
Step 2When the juice is strained, add the lemon juice and enough water to bring the volume up to 18 ounces (500 mL).
Step 3Cut the leaves of gelatin into a few pieces and place in a heatproof bowl. Add a few tablespoons of the juice mixture so that the gelatin is just covered. Soften the gelatin for 10 minutes while you bring a small pan of water to a simmer. Place the bowl of gelatin over the simmering water and stir from time to time until it is totally melted. Pour the remainder of the juice mixture over the gelatin, stirring to combine, then strain into a jug or other container.
Step 1Chop the gelatin into a heatproof bowl and add the water, along with the sugar and lemon zest. Wait 10 minutes for the gelatin to soften and then heat over a pan of simmering water until the gelatin has melted.
Step 2Once the gelatin has melted, add the milk to the bowl, stir to combine, and pass the lot through a sieve and into a jug or other container.
Step 1Pour a layer of blancmange into the mold. Place in the refrigerator until set. This should take only 15 minutes depending on the thickness of the layer.
Step 2Continue adding and setting contrasting layers to the mold until it is full. You can make the layers as thin or thick as you like. Thin layers set more quickly, but you will need to pour more of them; thicker layers set more slowly but there are less of them to do. When all of the layers are complete, continue to let the gelatin chill until firm before unmolding and serving, at least 2 hours.