Spread the damsons in a 2 litre shallow dish and sprinkle with caster sugar.
Preheat the oven to 190°C.
Sift the flour, baking powder, 100g sugar, and salt into a bowl.
Work the butter into the flour mixture until it resembles fine breadcrumbs.
Beat the egg into the buttermilk and mix into the dry ingredients to form a sticky dough.
Drop walnut-sized spoonfuls of dough over the damsons.
Sprinkle the topping with flaked almonds and the remaining tablespoon of sugar.
Bake for 30-35 minutes at 190°C until golden and bubbling.
Cool briefly before serving with cream, custard, or crème fraîche.