Preheat the oven to 400°F and set a rack in the center.
Peel and chop the oranges into small pieces and place them in an oven-safe skillet.
Add sugar, cornstarch, and lemon juice. Mix and let sit.
Grind saffron threads and mix with the melting ice cube to release flavor.
In a food processor, combine flour, sugar, butter, cardamom, cinnamon, and salt until crumbly.
Transfer to a bowl and mix in oats using your hands. Chill briefly.
Drizzle saffron water over the orange mixture.
Scatter crumble topping over the oranges in chunks.
Bake the Orange Saffron Crumble for 30 minutes at 400°F, then reduce to 375°F and bake for 35–45 minutes until golden and bubbling.
Cool for 10 minutes before serving with ice cream or cream.