Place the almonds in a food processor and whizz until finely ground. Set aside. Heat the milk in a heavy-based saucepan to boiling point. Mix the rice flour with the measurement water in a small bowl to form a smooth, thick paste. Take the milk off the heat and stir 2 tablespoons of the hot milk into the rice flour paste, then tip the mixture back into the milk, stirring continuously to prevent any lumps forming.
Return to the heat and cook gently, stirring continuously, for about 5 minutes until the mixture begins to thicken. Add the ground almonds and sugar and cook gently for a further 15–20 minutes, stirring occasionally, until thick. Meanwhile, dry-fry the sesame seeds in a small, heavy-based frying pan over a medium heat for 1–2 minutes until they emit a nutty aroma.
Stir the almond extract into the milk pudding, then pour into 4 serving bowls and scatter over the toasted seeds. Serve hot or chilled.