Combine 350g blackberries with 50g sugar in a small pot set over medium heat. Stir till the berries release their juice and the sugar is melted. Add the juice of ½ lemon. Lower the heat to a simmer.

Whisk together 2 tsp cornstarch with 2 tsp water till smooth. Add to the blackberry sauce, and stir till thickened slightly. Remove from heat. 

Serve with pancakes, vanilla ice cream or Greek yogurt.