Place the almonds and water in a blender and blend together to break up the almonds into a relatively fine pulp. Gently shake to mix the almonds through then leave the mixture to soak for around two hours, or a bit longer if you can.
After the almonds have soaked, strain the mixture through a very fine strainer - if your strainer is not very fine then also line with a cheesecloth - to remove all of the solids. You will in effect get almond milk. Discard the almond solids.
Set aside ¼ cup (60 ml) of the almond milk in a small bowl and add the corn starch. Stir to form a smooth paste then set aside. Place the rest of the liquid in a heavy based pan. Add the sugar, cinnamon stick and lemon zest strip and place the pot over a medium-low heat.
Stir the mixture now and then to help the sugar to dissolve as the mixture warms. Once the sugar has dissolved, re-stir the corn starch/corn flour paste and add this to the pot. Stir either as you add it or immediately after to help avoid lumps forming.
Continue to warm the mixture over a medium-low heat and stir constantly to avoid getting thick lumps forming at the bottom. If you do accidentally get a thick bit, press it against the side or bottom and stir to help incorporate it again. Keep warming, but avoid the mixture from boiling, until it thickens up enough to coat the back of your spatula. This may well take around 15 minutes since you don't want to have the heat too high. Once thickened, remove the mixture from the heat.
Pour the mixture into ideally two individual dishes (you can also use one larger then share or serve from that, though it doesn't keep it's shape so looks less pretty), straining to remove the lemon, cinnamon and any lumps that may have formed. Carefully cover the top of the dishes to try to avoid a skin or contamination and let the mixture cool to lukewarm before then transferring to the fridge. Cool for several hours (at least four, but ideally overnight) to allow the mixture to chill completely and firm up a little. You can serve warm or room temperature, but I think it's best served chilled. Top with a sprinkling of cinnamon before serving.