Sweat the onion in the butter until soft and translucent. Add the beetroot, orange zest and juice, caraway, vinegar, salt and pepper. Cover and simmer for 5 minutes. Transfer to a blender then add the gelatine. Purée until smooth. Leave to drain through muslin.
In a food processor, blitz the oatcakes with the melted butter. Spread over the base of a springform tin, pressing firmly. Place it in the fridge to set.
Beat the cream cheese into the drained purée. Whisk the egg whites until they hold soft peaks, then fold into the mixture.
Spread evenly over the biscuit base then chill it in the fridge again. Once set, gently warm the drained juices and pour them over the cheesecake to glaze. Chill it in the fridge once more until required.