Make the damson sauce: Put the damsons in a pan with 200ml water. Bring to a simmer and cook gently, stirring regularly, for 10-15 minutes, until the fruit has collapsed and the stones have come free. Tip into sieve and rub through with a wooden spoon to remove the stones and skins. Sweeten the damson puree by whisking in sugar to taste - how much sugar you need will depend on the tartness of the fruit and your personal taste. Leave to cool.
Heat the oven to 170C / 335F / Gas Mark 3.
Prepare the cheesecake: Butter a 20cm springform cake tin. Beat the cheese with a wooden spoon until smooth (if using unsalted goat's cheese, add a pinch of salt). Add the melted butter, oatmeal (or semolina or flour), 100g sugar, eggs and orange zest. Mix well. Spoon into the tin and smooth the top. Bake for 25-30 minutes until just set.
To serve: Cut the cheesecake into wedges and serve warm or at room temperature, with generous spoonfuls of the luscious purple sauce ladled over the top.
