SEVILLE ORANGES AND PISTACHIO BREAD

2 Seville oranges, scrubbed • 140g unsalted butter, softened, plus extra for greasing • 525g strong white bread flour, plus extra for dusting • 240ml whole milk • 125g golden caster sugar • 2 tsp fine salt • 2 tbsp cornflour • 7g sachet easy bake yeast • 2 eggs, lightly beaten • 2 tbsp demerara sugar • 100g unsalted, shelled pistachios, roughly chopped