Preheat oven to 350 deg F. Line 9 inch spring form pan with parchment paper.

Bring milk, vanilla, lemon rind and 1/2 cup sugar to a boil in a large saucepan over medium-high heat. Reduce heat to medium-low and add rice. Simmer stirring occasionally until rice is al dente and mixture has a creamy consistency, 20-25 mins. Remove from heat and let cool to room temperature. Discard vanilla pod and lemon rind.

Electric mixer - Beat eggs, remaining sugar, vanilla extract and lemon juice until pale yellow and frothy, 12 mins. Start at a slow speed and once ingredients are combined increase to high speed.

Stir some of the egg mixture into cooled rice to loosen it. Gently fold in remainder of egg mixture to form a smooth batter. Stir in Amaretto and mix well.

Pour batter into prepared pan and bake until top is light golden and cake is set, 60 mins. Sprinkle with lemon zest.