Preheat the oven to 180°C (160°C fan). Grease and line a 20cm springform tin with baking parchment.
Mix the crushed digestive biscuits with melted butter and salt. Press firmly into the base of the tin and chill for 30 minutes.
Beat the cream cheese until smooth, then mix in the caster sugar and vanilla extract.
Add the eggs one at a time, followed by the sour cream, flour, and salt. Mix until smooth.
Pour the filling over the chilled biscuit base.
Bake for 50–55 minutes, until the edges are set but the center still has a slight wobble.
Turn off the oven and leave the cheesecake inside with the door slightly open until cooled.
Meanwhile, roast the rhubarb with caster sugar, water, orange zest, and orange juice for about 15 minutes until tender.
Cool the rhubarb completely, then spoon it over the chilled cheesecake.
Refrigerate for at least 4 hours, preferably overnight, before slicing and serving.