For candied cumquats, combine caster sugar and 300ml water in a saucepan and bring to the boil over medium-high heat, stirring to dissolve sugar. Add cumquats, reduce heat to low and cook until transparent (25-30 minutes).
Preheat oven to 180C. Bring 1 cup water to the boil in a small saucepan. Add semolina in a thin, steady stream, whisking, until incorporated. When bubbles appear, remove from heat and pour semolina onto a plastic tray to cool.
Using an electric mixer, beat ricotta, icing sugar, 1 egg and 3 egg yolks, lemon rind and nutmeg until combined, then add semolina and beat to just combine.
In a separate bowl, whisk eggwhites until soft peaks form. Fold through ricotta mixture, then spoon into a buttered and floured 1½-litre pudding mould and bake until cooked through, when a skewer withdraws clean (35-40 minutes). Invert and serve immediately with candied cumquats.