Step 1 Make the ice cream: In a small bowl, stir together the cornstarch and ¼ cup of the milk to make a slurry. Step 5 Make the sauce: To a small pot over medium-high heat, add the berries and sugar and cook, stirring frequently, until thick, about 8 minutes. Place a fine-mesh strainer over a small bowl, then strain the mixture into the bowl, pressing on the solids to extract as much liquid as possible then discarding the solids.